You have to confirm your resignation. At least on the web interface; I haven't played on mobile for a while but I'm sure it's the same there.
So, it's not like the player accidentally resigned. Removing the option, even in cases like that, would either force the player to continue playing or just abandon the game instead of just resigning like they can do now. It doesn't really matter if resignation at such a point makes sense or not.
I believe my opponent in this game mistakenly hit the resign button when he meant to hit the draw button here which would have offered a draw in this scenario after black's 50th move. However, when he hit the resign button, he lost the game in a perfectly drawn position. There was no way for white to lose the game (even on time as black had just the bare king). So to make matters more fair, I think a good idea is to remove the ability to resign when the opponent has just his bare king.