You could take it at face value. I have no idea if this was a 15 minute off-the-cuff effort, or a larger researched project. Rather than assume they either did or did not know, I asked. If they knew, they can explain their choice more. If they did not, they have something new to look into.
If you are taking it as condescending, that is on you. It was simply a question.
The best way to look at it is that "are you aware" is always condescending. There are two answers; yes and no. If they say yes, they have to apologize for not adding your feature. If they say no, you're calling them ignorant. There isn't an out that deescalates and reduces the toxicity, so you're forcing everyone to now be as rude as you.
Phrasing your statement like "my corporate year starts on November 15th; is there any way to offset the start of the year?" would sound nicer. If the author was aware of that and didn't add the feature, then they can say so. Or if they weren't aware, they can say "good idea". Now nobody has to get defensive and the heat of the conversation can generally decrease, keeping everyone happy and polite.
> If you are taking it as condescending, that is on you.
Tone is an essential, unavoidable, yet undefineable thing. There's a geek fantasy that humans communicate logically and explicitly using only literal meanings of words, but the reality is that most human communication is in body language, tone, emotion, context, and more - and there's no way to define exactly how all those work or what they mean.
I got the same impression as the GP. I'm not always great at it myself but unless I make sure my tone conveys what I want it to convey, I'm rolling the dice.
If you are taking it as condescending, that is on you. It was simply a question.