Rats.. sorry to hear about that Camo, it sounded like the bike was running great. I figured if you ran the bike hard at sea level any elevation change would have been up, and worse case senario was the bike would have been too rich.
I don't want to make any accusations, but if you don't think your brother could ride the bike any harder than you did...
Is it possible the fuel can of pre-mix got swapped out for the straight fuel?
If I understood you, your last ride out was at the beach, so I'm figuring you were able to "See what she Had".
The sand / dunes puts a about as hard a load on a bike as you can get.
If the bike held together under those conditions, with you piloting, I don't see how running the woods was any harder on the engine. Now I don't Race and I'm certainly no engine guru, but I know it wouldn't take long to muller up the top end with little to no oil, the bike was jetted for sea level and it wasn't much cooler at 2500' than it was at sea level a few weeks ago. (well not enough to cause the bike to be jetted too lean at 2500')
Sorry Mate, I was hoping the plug just worked its way loose!
Tuck\o/