[bishop]

The ruling is correct, I would enforce the call once the bet amount is announced.

Verbal declarations are binding, I once enforced a player to call when he announced "if any of you push all in I am calling!".

There were four people in the hand, on the river and he was last to act, he also has the chip lead.

Mid position player pushes all in and I enforce the call from the last to act player, I then also sit him out for one orbit for angle shooting (influencing play with comments).

I think the above scenario can be debated more hotly than what occurred in OP.