I knew about the French. But since Irish is not a Romance language, I'm constantly surprised by the Irish words that actually are cognate (as opposed to more recent borrowings). So what struck me was how much ubh sounds like œuf, and the fact that it's not a coincidence. Since, as you said last month, ubh is cognate to ovum but not descended from it, that suggests to me that the parent word probably traces back to Proto-Indo-European.
(I've dabbled in a number of languages, but Irish is the first Indo-European language I've studied that isn't a Romance language. So I'm not really sure what to expect on the scale from similar to different.)
MOST of the words of Irish are cognates of words in other Indo-european languages. Being a cognate does not necessarily mean being a borrow word. Being cognates only means that two or more words have a common ancestor. "Egg" in English and "ovum" in Latin both descend from "owyo" in PIE (Proto-indo-european). It should be no surprise to see words that are similar in Irish, seeing that these languages are all descendants of PIE.
While Irish spelling is fairly regular, from a phonetic point of view (and taking dialect differences into account), it's not rigid, and older, simple words are often the ones that differ most. ubh has a "v" sound in all regions, but dubh only has a "v" sound in Munster.
The key thing to remember is that written orthographies are only guidelines.
In Connemara, generally, it depends on where in the word the sound is. At the end of the word, or before a consonant, it is sometimes pronounced as /v/. Unless, of course, the unlenited form would've needed an emphentic vowel, in which case it is /u:/. Such is the case in garbh, marbh, etc, where it would be said "garabh", but became "garú". As for dubh, it's more just the final sound is occasionally elided, but it doesn't elongate the vowel like it does in Ulster. So you get something that sounds like "du" instead of "dú", which is actually the /w/ following it in Ulster.
So, really, it depends on dialect and position in the word, as well as what vowels and such proceed it. It's not that what you learned was wrong, just that it doesn't tell the whole story.
When what you read conflicts with what you hear, assume that what you read is wrong. Written descriptions never describe all the exceptions fully, and can only be taken as approximate guidelines.
In this case, "ubh" has an "v" sound in all dialects, whereas "dubh" only has a "v" sound in Munster Irish, and a "w" sound in Ulster Irish, and is just "du", with neither a "w" or "v" sound, in Connacht Irish (at least some speakers of Connacht Irish - the speaker on Duolingo pronounces "dubh" with a "v" sound).
And while the Caighdeán has no formal standard pronunciation, most "non-dialect" speakers pronounce "dubh" with a "v" sound.
Even today the vast majority of the time someone says eggs without further qualification what they're referring to is uibhe circe. Furthermore even if the variety of eggs available to consumers has vastly proliferated since his day I don't see how his point is undercut at all. He notes that in his day, native speakers tended to explicitly state which kind of egg was being discussed e.g. ubh circe or ubh lachan etc. to the point that it was unusal to here ubh alone. The only thing having Cadbury creme eggs around should have changed is now ubh uachtair is added to the lexicon.
I don't mean to suggest that there's anything wrong with what's here in this exercise. Egg is certainly the correct translation of ubh. I just felt like since one of the most important speakers of modern Irish explicitly commented on this word it would be worth mentioning his thoughts here.
I did a bit of research, and "ubh" is not a borrowed word at all. It is cognate with the French "oeuf" because both words trace back to the same Proto-Indo-European word. The Celtic languages are every bit as European as the Romance and Germanic languages.
Broad bh is "v" in Munster Irish. Ubh is pronounced with a "v" sound in all dialects of Irish. Ulster Irish speaker might prefer to spell it ibh, but ubh is the widely accepted spelling.
While the pronunciation of Irish generally is more faithfully reflected in the spelling than English pronunciation, never assume that an otherwise competent speaker is doing it wrong because their pronunciation doesn't match your interpretation of a written guide to pronunciation. Apart from the fact we have a fairly standardized spelling in spite of significant dialect variation, certain words, particularly the kind of words that children learn to say before they learn to read, can have distinct pronunciations that will not conform to spelling norms, because it's the spelling that is the problem, not the pronunciation.