How many of our Baptist members are aware of our many (different) Baptist beliefs?
...Some of them proclaimed doctrine I had never heard about. - ie Closed communion - So if was a member for several years - and did not know all basic doctrine - they it be no surprise if a RC was aware or even concerned of such doctrines.
Closed communion is the church leadership's attempt to ensure that those receiving communion are in compliance with the following scripture. If the participates are members of a conservative Baptist assembly, their testimony is that they have been born-again - the fundamental requirement for receiving the elements without condemnation. However, being a Child of God does not, by default, make you worthy as indicated in verse 30.
1Co 11:27 KJV - Wherefore whosoever shall eat this bread, and drink [this] cup of the Lord, unworthily, shall be guilty of the body and blood of the Lord.
1Co 11:28 KJV - But let a man examine himself, and so let him eat of [that] bread, and drink of [that] cup.
1Co 11:29 KJV - For he that eateth and drinketh unworthily, eateth and drinketh damnation to himself, not discerning the Lord's body.
1Co 11:30 KJV - For this cause many [are] weak and sickly among you, and many sleep.
The Baptist church I attend does not invoke this scripture prior to serving the elements. I speculate the reason is because they do not want to offend those in attendance.