two gun mojo
Two Gun Mojo is a tough thing to pull off. But it can, and has been done. Certainly, not everyone can do it. But we all agree there have been and are "trick" shooters who can do it.
Well, none of them ever woke up one morning fully skilled. They all have to practice, a lot.
we've got a few slightly different things in the discussion,
2 gun mojo is unsafe
2 gun mojo is unsafe at an indoor range
2 gun mojo is unsafe at the range I'm at...
and then there is specifically what the guy did in the OP.
The guy could have been a fool. OR he could have been on his way to being the next Ed McGivern or Jerry Miculek. We just don't know. So a blanket condemnation of 2 gun mojo seem out of place to me.
Someone doing 2 gun mojo,
and lacking the skill to do it safely is certainly a bad thing, and even worse on an indoor range.
When you see someone doing it, odds are high they are either foolish, or just having fun. (and if the idea of having fun while recreational shooting offends your sensibilities, well, "Lighten up, Francis!"
The world is full of "experts" who are experts only because they think they are. Odds are high you'll meet some. But it is also possible that guy doing that "foolish" thing, is actually competent, or even expert. Only observation of what they can actually do will reveal the truth.
Sounds to me like the guy in the OP was irresponsible. But I didn't see it myself, just have to take it at your word. Good chance the guy doing 2 gun mojo is being an idiot, BUT that doesn't mean everyone who does, is.