[Force1]

im willing to bet the dads niceness and the owners rudeness are both overstated. i would imagine the exchange when somerthing like this

dad: yes, i was told you would sing happy dbay
owner: no sorry we are trying to change image we dont do that anymore
dad: but i was told you would do it
owner: i apologize about that but unfortunetly we have dont do that anymore and you shouldnt have been told we would

this should probably be end up continued on like this
dad: but i was told you would by your hostess, my kid is going to be upset
owner: listen, i apologize that the hostess told you that but we dont do that anymore
dad: but we were told it would be part of the dining exp.
owner: we dont do that anymore

probably carried on like this for a while until things starting getting more rude and forceful

this situation sucks but after finding out they dont do that anymore and the hostess made a mistake its easier to just drop it

also, im willing to bet those siding with dad have kids, and those siding with owner don't