I think the 1 nap is a fluke. 9 1/2 months is REALLY young to transition to 1 nap. Yes, it can happen this early but it is the exception not the rule.
Instead I see you have lots and lots of A time to extend before your son is truly ready for 1 nap. We typically find that a child is ready for 1 nap when they can handle 4.5-5 hours of A time. Right now you're putting him down for nap at 3 hours A time. There's a BIG difference between 3 hours and 5 hours! My guess is he's UT at 3 hours so that's why he played. Then you pushed him too long and so he was OT and then he just collapsed at noon for that longish nap. That will work 1 or 2 days in a row, but then he'll get in an OT cycle and nights will start to fall apart.
Better to go about this systematically: slowly stretch that first A time until you find where he's comfortable. We now know 3 hours is too little. So let's try 3h15 for a day or two, then 3h30, etc. -- stretching by 15 minutes every 2 days until you find where he's able to nap. At this age, babies on average like about 3.5 hours A time, so sounds like he's right on track! If you try to do 3.5 right from the start chances are it will backfire, so build slowly over the next 4 days and I suspect he'll nap for you at 3.5 hours A time.
This is a VERY common time for naps to start going a bit haywire. But I think with some patient A time stretching you'll have 2 more naps for at least a few more months!