I have not worked on an airline but as a sootie I would say that that was a very stupid thing to do. If you look at the flame, particularly towards the end it is at the bottom of the jet pipe. This is because the fuel puddles there when you have a 'wet start'.
If you have cranked the engine over a few times with the fuel valve open you can fill the combustion chamber. Most of this will fill a drains tank that will empty through a pipe out the back of the engine. (You can see this right at the end of the video).
The easy way to clear this fuel, and the lazy way, is to just start the engine and burn it off. The proper way is to drain the tank and dry crank the engine to clear the residue.
Of course, they may have simple of had a start up snag that cleared, (although I would not have sent the aircraft out without investigating it first)!
Inhibiting oil very rarely lights up, you just get a hell of a lot of smoke followed by possibly a small flame and slightly higher start temps. Again, this should be avoided by bleeding the fuel system first. This is almost certainly fuel coming out.