To be fair it is possible. I shared this capture a while back of a 'test' of various ransomwares (in Win 7). Note that some are caught by UAC, but some are not. Maybe the ones that were caught didn't do as much damage though, I do not know.
Privilege elevation through the use of an exploit and asking the user to elevate are two separate things. I think he's talking about the former because he said "regardless of UAC".