This might be a stupid question but here goes: how come the emphasis is not on fúm since that seems the important piece of information but on an scéal?
Am I to deduce that prepositions are never stressed, even when personally declined (if that's the correct term for faoi becoming fúm)?
Or is the emphasis in this sentence suggesting something like "It's the story which is about me, not (for example) the song"?
I hope I'm not overthinking all this but it all comes down to the fact I would have read the sentence stressing the preposition as in Tá an scéal fúm and want to know if that would be wrong.
In English, the intonation of the sentence would depend on whether you were saying "the story is about me (not you)" or "the story (that you heard about someone doing something embarrassing) is about me" or "the story is about me (but the song isn't)". The first example would usually have a stressed "me" in English, and fúmsa in Irish, but because even native speakers are fully fluent English speakers too, it is quite normal for fúmsa to be stressed too, but a stressed fúm without the sa would be béarlachas.
I wouldn't read anything in particular into the intonation in any single exercise, unless the text unambiguously supports it - the reader had to read thousands of these sentences, and probably had to say them a number of different times, and then someone picked out the one that sounded best.
"It's a story" is linking a pronoun ("it") to a noun ("story"), so you use the copula - is scéal é.
"It's a story about me" is is scéal é fúm (or is scéal fúm é - you could probably get away with either, though there is a slight difference of emphasis). scéal fúm is ea é is another possibility.
"There is a story about me" isn't a copula, so you use the verb bí, (tá in the present tense) - Tá scéal fúm. In some contexts, it might be better to say Tá scéal ann fúm.
And to wrap all that up Tá scéal fúm ann could be loosely translated as "There is a story about me".