I don't know what it is but take the hint. Find another place to drill. It could be a plate protecting something, or a pipe.
Yeah, I'll try drilling somewhere else. I wasn't too specific but given the location of that wall, I know for a fact there is no kind of pipe or anything in there.
If it was concrete in the floor I would guess rebar
Rebar is used in hollow block wall too:
I'd remove one of those circular knockouts at the back of the wall box to drill an inch to the left or right.
Huh, the more you know. I'll try that out tomorrow. Thanks
Judging by how far it looks like your bit drilled through the wall it could also be that you were just having the absolute worst luck and managed to find a brick tie on your first attempt. If that's the case then the good news is that you shouldn't have a hard time avoiding them if you stay around the area you've already drilled into.
Might be rebar or other reinforcement in the wall. See if you can shine a light on the hole and see what you are hitting. You might have to vacuum or blow the dust out first.
For DIY - this is also a placeholder.