Looking to install new tile in an existing second floor laundry room. Condo was built in 1979. The laundry room is currently tiled.

I popped up a cracked tile and found about 1 inch of concrete directly under the thinset - I was not expecting this. I believe the subfloor is under that. I am completely new to this and here's my question. Should I attempt to fill the cracks in the concrete and tile over that (seems to be hairline cracks so far) or do I need to rip out to the subfloor and start fresh. Why would there be an inch of concrete on the second floor? Any advice is appreciated.