I'm sorry....I am a bit confused and a lot doubtful.
You put 190-200*F water in the cooler, (by the way, if your hot water is really that hot, wow. My hot water tank, turned up very high, is only 145), and closed the lid and let it sit for 30 min.
Then you dumped out the hot water, added grain, and added 165*F strike water?
It's absolutely impossible that your mash hit 189*F then. Even if the cooler really was preheated fully to 190*F, it just doesn't have the thermal bulk. Sans grain, I'd be amazed if a 190*F cooler could head 165*F water up more than a degree or two. With 70*F grain, it's just patently impossible.
Either your thermometer is borked, (this is my guess), or you are magic. When you say you have a nice digital thermometer, is it one that looks something like this?
If so, if you get ANY moisture in the part where the wire enters the metal probe part, it will read anything from -200 to +500*F. Could this be your issue?
Also, after adding strike water, wait 10 minutes before taking a temp reading. It takes a while for everything to equilibrate.