I used a warming lubricant to give my boyfriend head and after we were done he washed it all off and layed down in bed and he was burning up "down there". Is is normal for that to happen even after the lube is washed off?
I've heard of that happening. Hasn't happened to me with warming lubes specifically (I've used only one, Sliquid's Sizzle, and it wasn't actually warming...? Anyway...) but with lower-quality lubes.
Depending on the lube you used, and I'm specifically thinking of Intimate Organic's flavoured lube line here, it may have left a residue on his skin. The reason I'm thinking of IO's lubes is they don't actually contain any water, and they're kind of oily/greasy. I've had some spill on tile flooring, and it left an oily sheen on the floor even after mopping.
Or he had a mild allergic reaction to something in the lube. He could try putting a little on the inside of his elbow to see if he has a reaction without putting his genitals at risk again.