In my 25 years of following pro cycling I have never seen anything like this. It is just unconscionable that a professional rider would be so foolish and so negligent to do such a thing. Whomever said this looks like a bad Cat 3 or Cat 4 finish is right. There have been plenty of stupid crashes through the years from bad judgment, but never anything like this.
Crashing other riders due to poor riding has happened, several times. Going from memory, Djamolodin Abdujaparov made a habit of crashing himself, and sometimes others. And here are some of the worst, but never have I seen someone grab someone else's jersey out of panic (or otherwise) and not let go until they had both crashed to the asphalt.
In the 2003 rain soaked Giro Mario Cippolini was crashed by Issac Galvis while going around a corner and both went into the barriers. Isaac nodded in acknowledgment of his mistake when Mario shook his finger at him.
In the 2002 Giro Francesco Casagrande foolishly rode Freddie Garcia into the barriers on an uphill finish and was banned from the race. But Casagrade had both hands on the handlebars and stated they tangled while Garcia was trying to pass him on the inside. Casagrande was in 4th position and contending for GC at that time. they tossed him anyway. Still, he didn't grab the guy's jersey.
In I believe the 1996 Giro two riders were in a heated argument on a remote climb when one of them tried to nudge the other off the road. It didn't happen, but he was immediately banned after the stage. However, he did keep his hands on the handlebars the entire time.
I have never once seen anyone do what Theo did. Not once. Whether it be from subterfuge or total negligence, there is no room for actions like this in the sport.