Alternatively: It doesn't matter because he is wearing that diaper, so he can just go where he's standing.
My bet is on him deliberately trying to lose bladder control by holding it until he can't. Unless there's some context that I missed. (Obviously, there's many possible courses of events that could have led to this situation, this is just my own preferred interpretation.)
Alternatively: It doesn't matter because he is wearing that diaper, so he can just go where he's