You based a lot of your actions on incorrect information. Just because you shut your PC off doesn't mean it stops moving electricity across your board. You can still short your board or any device while it has access to power so "shut off PC before it could short" was incorrect. But you learned this as you can see it had already done "something" by causing power cycles.

Compressed air would spread the water out rather than dry it out, though yes it could dry faster. And a few hours is just being impatient. You seem to take shortcuts before actually taking the proper steps (shutdown>completely unplug & wait few hours>"let it dry a day or so"). You probably could have done less damage or none if you took your second steps first.

Problem isn't the H2O, it's the minerals/contaminants that remain even when the water evaporates- unless it was distilled. Ex: If you pour water at the center of a paper towel and let it dry out, you will always notice the ring and color difference between the inside and outside of the ring. That's what will cause your shorts. By blowing the water with compressed air, you actually increase your chances of something being shorted as you just spread contaminants all over the board. It is also easier to clean with isopropyl alcohol if the water isn't everywhere and is concentrated in certain areas.

Sometimes the residue left behind wasn't big enough to cause any shorts and when everything is properly dried and all the contaminants/minerals shrink after losing their water content, your PC starts fine.

If you want to be 100% thorough, google up how to clean spills on electronics. This is going to take time and effort so it's up to you. You can decide to do a thorough cleaning or just say what the hell and just try turn it on and replace it if it's bad.