For the sake of information, that priest was way out of line. Church law does require that which was discussed earlier, but free will allows priest and layman to accept or reject that law.
"Communion indicates a union with a particular group of people or organization, in this case, the Catholic church, in addition to the celebration of the Lord's Supper."
This is correct. This is also why a Catholic is not supposed to participate in communion at a protestant church. A Catholic who is trying to follow the faith they profess cannot, simultaneously, be one with any other Christian faith. Too many, IMHO, do not understand or appreciate the magnitude of the Lord's Supper, whether Catholic (who are supposed to discern the Body and Blood of the Lord) or protestant (who are just supposed to take it very seriously, I think).