Sounds like you might have a pocket of air that's landing on the coolant temp sensor and causing a super high reading.
The bolt above the thermostat is great for getting air out of the head, but it is not the highest point in the system.
It's actually not even the highest point in the cylinder head, when bike is on side stand.
The rad cap is higher than it, but when bike is on its side stand, the highest point is the top right (as you sit on the bike) corner of the rad.
The optimum way to drain the coolant (imo - this bit isn't in the manual) is to tilt the bike to the right (as you sit on it) and prop it up using a short length of say 2x4, under something secure & solid on the lower RHS of the engine.
Then the rad cap is the highest point in the system, and the bleed bolt is on the high side of the cyl head.
Now ready to fill the system, via the cap.
The bleed bolt above thermostat can be in a couple of threads only as you fill, and once coolant starts coming out there strongly, thread it in fully& nip it up.
For good measure, a couple times as you fill, rocking the bike from right to left and back again to the prop is good for shaking air pockets loose and over to the rad cap.
Once the system is completely full up to rad cap and no more air pockets appearing from rocking - fit rad cap, and then fill expansion bottle to the high mark.