Title insurance insures against flaws in the title to the property that he bought. Assuming the legal description in the deed and in the title police match the address he bought - he has insurance against title defects in the chain of ownership, of the unit he purchased. The fact that he was given keys to the unit next door and that he and the agent made an error in identifying the property, does not mean he has a title claim.
I wonder why someone would have keys to give someone for a property they were not representing.
You are correct sir. As noted by others above, the buyer’s recourse is to Coldwell Banker, which, luckily for him, is one of the realtors still out there that is in business and has assets. He will get compensated—probably has been already, since this story is from March.