I've unfortunately seen this sort of thing before, and it's a tricky one to deal with.
Because the child had serious developmental issues, the parents didn't feel they had to work on discipline or behaviour -after all, there was a medical reason why the child couldn't behave. So you had a 7 year old who acted inappropriately, and was impossible to contain or control or redirect. People put up with it because after all, it was a developmentally delayed child.
Then the child grows up. And there's a *huge* difference between an inappropriately behaving out of control 7 year old, and a fully grown, sexually mature adult who with the behaves like an out of control 7 year old, one of the biggest being that they are physically bigger than the people they are running into, screaming at, hitting, inappropriately hugging, grabbing stuff from, and so on.
But if you don't invite the family, or you leave the developmentally delayed adult out of the invitation, or ask them to leave or control their behaviour, you get a massive temper tantrum (on the part of the parents) plus accusations that you're a bigot and hate disabled people because they're disabled, and are so meeaan!