What was the coolant level before the ride? If it was filled to just below the neck of the radiator filler opening, it's very likely to burp coolant when it gets hot.
The usual coolant level is maybe 5-6mm above the fins. Adding four ounces is not uncommon, but still more than normal after a burp. The best way to judge overheating is to look at the head orings. If they are squared up, then the engine has been very hot, hot enough to affect the rubber.
If the orings are stiff they have been royally baked and you need to inspect the piston for wear. It's also possible to have the rings sticking after an overheating scenario.
Your pictures don't show anything alarming. The plug looks typical with stock jetting which is on the rich side. The buildup on the electrode is a bit strange, but I've had my plug covered in black carbon after four years on the same plug.
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2011 EC250E
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