yeah well the site is very wrong especially about the all engaging in consensual sex simultaneously cause that sounds more like a polyamorous relationship
The site may have a different definition from what you understand of the term, but that does not make it wrong.
It just makes it different.
Whatever the site chooses for its definition, is correct for what the tag means on this site.
It's up to us, as members, to understand how they use it. We shouldn't just assume that our existing understanding is what the site uses it for.
Polyamorous just means having an open & intimate relationship with more than one person at a time, with consent from all.
Most (if not all) harems, in adult games, are polyamorous.