You're 100% right (2x right?), but I think this is one of those situations like "bimonthly", where people usually intend it to mean twice a month instead of eve

You're 100% right (2x right?), but I think this is one of those situations like "bimonthly", where people usually intend it to mean twice a month instead of every two months. It's completely ambiguous with potentially significant costs for misunderstanding, but people refuse to make themselves clear, just because.