Distribution electrician here. I have seen glowing connections like this and know other guys who have as well. Pass enough current through enough resistance and it's entirely possible.

That said, I am pretty sure that isn't what is happening here: For the primary current path to be through the nut that would also mean that same current was flowing through the much thinner washer, which would accordingly be glowing even brighter than the more massive bolt and nut. Not only isn't it, but also missing are any signs of spot heating along the edges of the wire lug where it makes intermittent contact with the bus due to an obviously poor connection.

TL;DR: While possible, I agree this looks bogus.