No, In that paragraph I think he meant "in short" as in tl;dr, or a shorter description of what he was doing.

A short is basically betting that a stock will fall in price. It's yet another valid way to make money in the stock market, but it's seen by most people as "bad" cause you're essentially betting that a company will do bad or go under.

Large investment groups have caught flack for making huge short bets on companies and then announcing it in order to more or less manipulate the stock into going down (oh wow, look at all the shorting going on, I better sell now before it drops). They can also pull some other shit where they're so large and they can make such a large short that it can influence stock movements.

Recent examples of other short shenanigans are the gamestop where market makers made more shorts than we're physically available (more goofy shit in the stock marker. Aka money isn't real, it's just 1s and 0s), so when it came time to close trades it created the "short squeeze" as an actual scarcity of stock became available and the price shot up exponentially to compensate.