It's actually because January is also misspelled. Or possibly because Excel's language/region isn't set up right (I see your month abbreviations aren't us-eng... If excel is in us-eng it likely isn't going to identify them properly.
Ironically AI would probably work ok here whereas excel is using a human-designed pattern matching heuristic that apparently either has a bug or didn't take into account your locale properly. I say that as someone with a relatively negative opinion of ai
This is a task ai would do well at whereas most of the Excel workflow it would not.
The language used doesn't matter and it's not a bug. I can't be arsed to set my whole office suite to English but this is what Excel does, no matter what language you're using. So if I used English month abbreviations, the same thing would still happen.