It's more nuanced than that though. The isolation period starts from when symptoms start, not from when a positive test result is returned (unless the test comes first). So players with a positive test returned on Thursday 16th could still be eligible to play on Wednesday 22rd evening if their symptoms started early enough to do 7 days isolation before the match.
Not saying it's impossible they are gaming the system, I agree it does look a bit sus as 'more cases' on Thursday would arguably have to have been existing cases just without a positive test in the above sceanrio, but as you've inferred, without full transparency it's we'll never really know if that's the case or not.