Crock Pot turns to "warm" before cooking time is done?

Hi all, I just used the Crock Pot for the first time today. I set the time on "High" for "4 hours", but I checked the machine an hour after putting in my ingredients and it was already on the warm setting (the manual says this means it is finished cooking). I'd open the lid to check if the meat is cooked but the manual says not to remove the lid within the first 2 hours.

Is it a faulty Crock Pot or did I do something wrong? Thanks