I think you may have to speak to the "organiser" directly. Possibly you and your husband and maybe one or two other owners ( but not a posse). Say that you realise there must have been some confusion as most people thought the party was being organised by the committee but you have been told that is not the case. If the invitation wording suggested that it was "official", explain they would be better not to word it that way in future as this is clearly a private party organised by this person.
You should tactfully say that, while they are entitled to invite whomever they wish to a private party, you would not be able to attend as the impression is that it is an officially organised party and you believe it will be divisive for the tenants to think they are excluded and not welcome. I would say that overall many people have banded together to support each other during this pandemic and you think this invitation to an owners-only party will undo some of that good work. You may have some specifics of how nice people are and maybe even of a time when the organiser needed support from others. It certainly doesn't seem to make much sense - I could understand excluding troublemakers ( maybe - and just as likely to be owners), but is this just snobbery? If so, on what basis? Many people of various backgrounds and income levels rent for all sorts of reasons, so even the "snobbery" logic is a bit weird! I hope it doesn't go ahead in its proposed format and lead to serious disharmony. Good luck!