Could it just be a thermostat....?????

Hope you are all having a great weekend.

My girl friends sled developed an overheat issue this weekend.
She has a 2001 700RMK with 3900 miles, and drove about 25 miles with no issues.
I did noticed some green spots in the snow under the front / middle of the sled. When we stopped, we kept filling the coolant bottle.
Then, the overheat warning light went off, and it went into limp mode.
The fluid bottle was pressurized, and after it cooled down, we filled the bottle, and started on our way, until the light came on again. At that point, we towed back to the trailer, got on another sled, and enjoyed the rest of the day.

Thought maybe the water pump,belt went, thermostat, heat exchanger was leaking, hose???

When I got it back home, pulled the thermostat, and it looked like the picture below. Could it be that just the thermostat just is bad? Could it be that easy???

Your thoughts are greatly appreciated, as was wondering if the overheat caused the thermostat failed, or if it caused the the overheat?
Thanks
Bob

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Could it just be a thermostat....?????