I mean this is just some blog, no? I guess quarters are technically a bit more inclusive, but it seems like small beans IMHO — the 12% of humanity living south of the equator is likely used to this sorta thing.

Maybe I’m just showing my northern bias?

I missed that it's a "personal" blog, but they prominently describe their position as the emoji subcommittee chair, so it's more or less an official outlet.

Northern bias, yes. What about emoji or Unicode is tied to the weather? Why not use more universal time markers? If dates or months are truly too precise for this timeline, quarters are good enough. They could also just have a month range or "approx".

Being near the equator (whether northern side or southern), I don't have an innate sense of seasons at all, so have to remember what people are referring to when they use these terms.

I like how SkillUp handles it in the This Week In Videogames show when talking about release days; basically says "northern summer" which acknowledges that the publisher said summer while clarifying whose summer it actually is (eg, not his, since he's Australia-based).