If you see a good post in the Low Quality review queue, simply click "Looks OK".
Posts can be placed in the Low Quality review queue automatically by the system based on various heuristics, or by another user flagging them. It takes more "Looks OK" than "Recommend deletion" votes to remove it from the queue.
Some such reviews are review audits, automated ...
The number correctly indicated the number of active review tasks, though not the number of tasks that you, personally, were eligible to review.
Checking each of them ahead of time to see if you're eligible to review them would be a lot of extra overhead, and the number could still be wrong in some cases.
I think this makes sense, even if it's not the most clear language: it's saying that you raised that type of flag (a close-vote-ish flag) already, not that specific one. It's not telling mods you raised both of those flags, don't worry.
And you can't vote to close a question for two different reasons, so it's pretty consistent that you also can't flag it ...