Yeah I think people in the UK and Europe see Multiculturalism as "tribalism", with completely independent cultures and communities socially-exclusive from each other. It has a very specific meaning in Europe.
People in US see it more as a mix of everyone together and influencing each other, which we describe more as a "melting pot".
Case in point - People are arguing two entirely different things.
"Multiculturalism is based on being openly accepting, integrating, and respecting other cultures. " - This is great. Most of us can hopefully agree on this.
" It absolutely doesn't have any tenants that cultures should be distinct, separate, and never interact." - It does in the UK and EU though, that's why we specify Multiculturalism and not integration. This is where the arguments (and maybe misunderstandings) are coming from.