Sounds to me like the folks who gave you trouble were either just being jerks or simply didn't know what they were talking about but felt genuinely concerned, or both.

They are correct that cats and monos do swing differently, but that has little to do with whether they will hit each other in a typical BVI mooring field. Regardless, unless they have approval from the owner of the mooring ball, they have no right to shoe anyone away from it. If they don't like it, it's up to them to leave. Sounds like your captain handled things appropriately.