Just because they held appropriate balance at one point in time doesn't mean they are actually sitting on dollar reserves corresponding to tethers. They could have borrowed to reach these numbers for the report.

The current state is still that the majority of Bitcoin volume comes from tether, and these tethers aren't regulated and required to exist the same way dollars traded for stocks are required to exist. They already mixed tether reserves with other funds in the past, don't trust them to suddenly stop.