Was this a 'Branch Meeting' ? IME these tend to be primarily business meetings and as such a new visitor may well find themselves sitting on te sidelines. However, a well run meeting will aim to include new attendees and certainly recognise their presence with introductions and an overview of the evening. In my local branch the monthly business meetings usually take just over the hour and are always followed by an informal social/chat in the bar afterwards.
If it is social activities you refer to, then there should be no excuse for not being made welcome. Being made to feel like an outsider is not pleasant and is unnecessary. It is hardly conducive to encouraging active involvement.
Whilst I wouldn't expect you to name the branch here, in which area of the country did this happen to you?
John B