Erm, it definitely has something to do with it, or at least it matters to the numerous people in this thread and many others who reference right footers cutting in from the left.
All it proves is he hasn't played there before. Attitude and willingness to adapt is a part of it, and on that we can only speculate, but his skill would mean he could flourish there. Plenty of players can flourish in a position they haven't previously played, eg De Bruyne being moved to a number 8, Firminho moving to a false 9, Bale moving from LB to LW to 10 to RW etc etc.... I trust my evaluation of Grealish's skill set over a simplistic analysis of he hasn't played there before so can't be any good there.