It's a very literal translation and awkward in English. According to google translate, "fueron unos diás" = "it was a few days." Now, I realize that it's not always reliable but this seems much better than "they are days."
I think that they mean "It was a few days with little snow." or "There were a few days with a little snow" or "Some days were a little snowy," or "A few days had little snow" or "It snowed a little bit on a few days" or "There was a little snow on a few days."
In the absence of any context, this translation borders on nonsensical (at least to a native speaker of North American English). Do you suppose maybe the "They..." is a typo for "There...?" Anyway, I think my translation, "There were some days with little snow" should have been accepted, so I reported it on 25th August, 2018. May John McCain rest in eternal peace.)
Duo accepted "There were a few days with little snow," but I think you are more nearly correct, Ryagon. For example, Speaker 1: "We came here to ski during the last week of January, but the skiing was terrible from Friday through Tuesday." Speaker 2: "Yes, they/those were some days of little snow."
EDIT: OR, Speaker 2: "Yes, they were days with little snow" (not translating the unos to the English, which is acceptable, I believe).
No, those expressions are not the same.
Fueron unos días. - "They were some days" or "It were some days", maybe? We have already talked about that group of days and are now referencing them.
Hubo unos días. - There were some days. We mention the existence of those days.
It's basically like "It was a day with little snow", but instead for multiple days. I'm not sure how English usually solves that.
This may very well be a sentence construct that would be considered normal in Spanish and maybe, possibly, in English, as a report of some type, a person might say, "These were days...." but I can't imagine any normal usage of the phrase "They were some days...." by an educated, native speaker of English.
Sometimes there are words in other languages that just don't translate from one language into another and I think this is a phrase that just doesn't translate from Spanish into English.