I don’t think it’s ideal, but it is ok as far as I know. I hope he did it over the ciborium though- so that any crumbs that might fall as a result of breaking the host wouldn’t land on the ground.
The sound of them snapping the body of our Lord repeatedly was very bothersome to me, although I cannot really see an alternative either.
I don’t think it was wrong for them to do this- Jesus in the Eucharist is not divided, although the hosts may be.
The nuns used to say that you were not even supposed to chew the host, is this act now acceptable?
It was never really forbidden, as far as I know. It is a pious act to refrain from chewing the Host, and the nuns you mention saw this and felt it appropriate to strongly discourage people from chewing the host- but it’s not required (I don’t think it’s even really addressed in church documents).
I have trouble breathing through my nose while I am walking, and I don’t want to breathe through my mouth with the Host still in it- sometimes I have to chew the host (I do it as little as possible) to move it along quicker so I can breathe without blowing crumbs on the floor.