What's behind my drywall?
but when I drilled it went in an inch before encountering a hard surface. Definitely not wood. I applied pressure and drilled, and it finally "broke through" in a matter of seconds


This could be bad depending on what you actually drilled through. It might be a good idea to open up the hole enough to see what is there, but do it without drilling and do it carefully.

Why could this be bad? If it was a metal plate installed to protect electrical wires, a wire itself, or if you drilled into a pipe*. You probably can't be sure until you take a look.

I would carefully try to cut a larger hole through the drywall. If you can cut a clean square around the area it will make it easy to fix, as you can cut a square of drywall and use it as a patch for the area you removed. You can possibly replace the square you removed.

You should do this using a drywall knife, or another sharp knife that allows you to make clean and controlled cuts.

If you're not that handy, it might be better to leave it as is, as you don't want to hurt yourself or do more damage.

Once you know what's there, then it's easier to suggest what to do next.