My initial thought is this:
WHY is this being said? Unfortunately, I've seen many small groups that develop a "we are God's chosen group" mentality (meaning "we are more special than everyone else"). That kind of mentality fosters pride... and eventually, elitism and cult-ish tendencies. (God chose this group for you so if you leave this group, you're missing God). If things are being said in that context, I'd be REALLY concerned.
If, however, it's said in a context of "God knows what you need, so He put you here at this particular moment to get what you need" with the understanding that we are ALL parts of the Body, and at some point you might need something else/God might move you to a different place... well, that's a much healthier POV, imo.
Small groups can be a really good thing. Isolationist/elitist groups can be a really bad thing. Why isn't the leader of this group plugged into other groups/churches, etc. so that he/she can also be ministered to/grow? Even the strongest part of a body will die if it's cut off from the rest of the body.