Wendy - actually believe it or not almost every time I've had a night like that it's been UT!! Crazy I know. They go down fine at night, making you think, oh good, it worked out and then their up in the middle of the night. Not enough A time before bed has been a constant issue with us on and off, but I didn't really realize it until the 2-1 nap switch. When we finally went on to one nap he was doing 5 hours A time before bed, no problem. Then we started getting these weird weird wakings, and I pushed back bedtime and they went away
I can't see how he could have been OT

He had less than 2 hours A time before bed. Where as he's been having way more A time before bed and you didn't get these wake ups

Sometimes just adding 15 extra minutes will make these wakings go away. But maybe I'm off base here.