So I just assume Karo knows (s)he plays this tournament?
The line is a bit vague for me then. What if X says: who wants to play doubles (and is ranked 31)? and someone else (with for example ranking 300) says doubles with X, can that also be seen as definite confirmation?!
I guess it's up to players to track these things and if they haven't agreed to that, turn up and say so.
In practice, it all seems to work fairly smoothly.