Isn't shorting entirely speculative and based on whether anyone is actually watching the stock closely?

What's correct about that sentence is that shorting is speculative. It's a type of contract a person can use, to their financial benefit, if they believe strongly that the market price of a stock or product will decrease.

Where they get that believe from, is irrelevant. I didn't follow the gamestop meme closely, so can't speculate on their believe.