I'm a handyman with not much plumbing experience; I do alot of deck repair, roof repair, fence repair, etc etc

My question is about the master bedroom shower and toilet in the house i live in. Person took a shower tonight and while in the shower he could hear gurgling so he looked around and found that while he was in the shower the toilet was gurgling and it was dirty water gurgling up. When he got out of the shower it stopped and he flushed the toilet and everything was fine.

I haven't snaked the toilet yet, but I'm guessing the toilet must be slightly clogged, Reason I'm here asking for opinions is because this house has had issues in the past with the cesspool filling too quickly and they had to have it pumped too often.

Does this sound like a clog or more of the cesspool being full, or something else entirely?