is this a big deal?

(throwaway account)
let's say there's an artist that you like and he did this:

he (21M) met a girl online (from another country) and they both start to like each other.
he sees in her profile that she was 17 and he asks when is her birthday.
she says in three months.
he assumes she will be 18 in three months and he decides to wait for the 3 months to ask anything romantic.
he finds out (a few weeks later) that she is actually 16 and she put "17" in her bio because her birthday was close.
he says "wow, we can't do it. you're cool and all but we can't date. let's just stay friends".
they just stay friends and send memes every once and a while.

is this a big deal? how would you react if a guy you're a fan of did this?