AMC Entertainment stock rocketed more than 50% higher on Thursday before paring gains a bit. But this time around, fellow meme stock GameStop wasn’t along for the ride.

AMC shares (ticker: AMC) were up 39% to $27.09 in mid afternoon, after setting a 52-week high at $29.75. GameStop stock (GME) was down 1.6% to $248.75. The performance gap likely isn’t due to differing views about the companies’ business prospects, but rather supply-and-demand quirks that are exaggerated by short interest, social-media excitement, and momentum-based...