If any tiny crumb of debris of any kind has plugged up the oil jet underneath the cam bearing on that side, this will happen. The curled-up rubber seal indicates very high temperatures occurred in that area when the oil stopped flowing.
There is a small oil metering jet underneath each cam bearing, toward the middle of the head, at the back side of the bearing housing(s). They are fed oil directly from the main oil journal on the back bottom of the cylinders, where you can see a cap on the right side of the engine. From the middle of this journal, in the center of the engine, there is a passage that goes straight through to the oil filter where the oil pump has pressurized that filter housing to push the oil everywhere. Troubles with debris in the oil system happen when the oil filters are either torn, installed backward (filter to the from instead of having the spring and flat washer push the filter toward the engine block), or someone lost the flat washer that fits behind that oil filter spring, letting the rubber get chewed up by the spring. Then, when changing the oil after that chewing had started, leaving tiny black rubber bits all around in the oil filter housing instead of cleaning it all out (not checking), the bits end up in the main oil journal, then move upward to block the oil jets, and the cam bearings lose their lubrication and seize. I've seen this series of events totally destroy these motors before, hence all the details.
I'd suggest pulling off the oil filter on the front of the engine. Look to see if tiny black bits of rubber might still be floating about in the area, chewed off a previous (or present) oil filter. Get the washer: PartsNmore and Honda still sell them. For the top end, you'll need another cam bearing with caps and a newer cam.
And flush out the oil passages manually if you have to: you must pull off the alternator cover on the engine's left side to see through the whole oil supply journal. Remove the camshaft and the cam bearings on the top of the engine and pull out (and clean) the oil jets. Flush downward with solvent spray from those oil ports into the main oil journal and let it run out the open cap and plug on both ends. Then plug the alternator end of the main oil journal and flush it through with solvent, which will then flow out the oil filter area on the front of the engine. When the engine is all put back together, put in 3 quarts of oil and re-prime the oil pump, then, using the electric starter and with sparkplugs removed (and your car's battery jumpered to the bike's battery to help with this, as the cranking times will be long, like 10 second bursts) restore oil pressure (Oil PSI light goes out) and flow (look into the valve caps to make sure you can see oil drooling down by the valve springs) to fill up the new oil filter and all the journals. Then drain all that oil, as it will likely have other black bits still in it, somewhere. Then install new oil and filter again.
BTW: this requires the engine be pulled out of the bike, as you cannot remove the cam cover on top without doing that first...
