I made a crockpot stew and the meat was dry and seemed mealy. Did it overcook?

I think ChefJune is on the right track. Some tougher cuts become wondrous with long slow cooking but leaner, drier cuts become just become well done and dry.

Did you sear it first?

what kind of meat did you use? Not all cuts are meant to have a long slow braise.

How long did you cook it for? And at what temp? Two things will dry out meat in a stew. Too much time and too high a temperature, both of which crock pots encourage.

http://www.seriouseats.com/2016/02/science-of-stew-why-long-cooking-is-bad-idea-overcook-beef.html