The mechanic installed the rebuilt head in a 2006 Ford Focus 2.0 DOHC. The #2 piston hit the spark plug when he tried to start. What happened?

Timing belt was installed incorrectly and the piston actually hit the valves. Time to remove the head again.

Ok, thanks for reply. The mechanic, an independent shop owner, took the head off and now says the number 2 piston is broken. He said he will repair it but now expects me to pay for the piston. In fact, he suggested replacing all 4 pistons. When I brought it in the first time, it was determined one of the exhaust valves in cylinder 3 had a chip broken. Which I saw and have a photo. So, the head was completely refurbished and reinstalled. Based on your answer, the timing belt was installed incorrectly I should not have to pay any extra. And if the piston hit the valves, I assume they are damaged, too. Is there a youtube video showing how to install the timing belt, (it's actually a chain in the 2006 Ford Focus 2.0 DOHC) that I could give the mechanic. Please advise.