This is a mistake that shouldn't happen. It means that someone commiting crimes could trivially hide and get the wrong person accused by using homoglyphs [0].
Generally when this happens, it's because they copied the Latin glyph and then made some tweaks to the whole Cyrillic alphabet to make it look more even, etc., and the changes to the 'a' may not even be intentional, but the 'a' got caught up in a batch change or something.
I feel otherwise: usernames and other identifiers (URLs particularly, and a number of other widely used identifiers), should be drawn from well-known, common, and small charactersets. The original 7-bit ASCII characterset (128 distinct characters), or some subset of that (e.g., Roman alphabet, Arabic numerals) may not be the native representation of all cultures, but it is all but certainly a familiar representation, and avoids numerous homoglyphic attacks.
<https://en.wikipedia.org/wiki/IDN_homograph_attack>
By contrast, Unicode has something on the order of 160,000 distinct characters.
<https://en.wikipedia.org/wiki/Unicode>
This greatly exceeds the typical vocabulary (distinct known words) of most native-language speakers, estimated at between 20k -- 35k words for a typical adult English speaker.
<https://wordcounter.io/blog/how-many-words-does-the-average-...>