He converted. He still wasn’t good enough. His ethnic background did indeed play a role in the priest’s decision to exclude him from the main chapel. Hence, his lifelong resentment.
I’d be really surprised at that, since normally getting a convert from another background was a real high point. It’s possible that the wedding was not very large and they didn’t want to use the main church or even rarely used the main church (I was in a parish at that time where virtually all weddings were in a side-chapel), or that neither he nor the bride’s family got along very well with the priest, who was therefore being vindictive (because normally even if the priest didn’t like one party, if the other party was a long-standing parishioner, that would win out). Or possibly the priest was a nut.
In any case, it would certainly have been uncommon, but if that’s what your father perceives, it may have happened. He should have complained to the bishop at the time, however, because the priest shouldn’t have been allowed to get away with this.