If what you say is correct then it all seems fine to me.
I am very sceptical that they ever drain the pool. It’s a lot of water. Most pools are NEVER drained. It’s just to expensive/slow/wasteful. Instead they get a chemical shock and a bit of a breather over winter. Which I do find a little gross, but I would think that they have researched the health and safety aspects and are confident that what they are doing is safe, even if it gives some of us the ick.
Having grown up in the tropics and subtropics with pools and dogs, the main problem is dog hair in the pump.