From your description of both the resistance in turning the plug and the plug's condition, it does sound as if it's cross threaded.
Because it was cross threaded, the plug didn't properly seal the cylinder allowing oil, air/fuel to blow-by and foul the plug.
It is something which should be corrected because you'll foul the plug and the valves, not to mention suffer performance and mpg. If you're lucky, it'll be a simple job of using a thread chaser -
Thread Chaser or worst case, a helicoil insert -
Helicoil
If you've never done this, or have any doubts, best to have a shop do it for you.
