If is very hard to figure out who is the writer/holder and what the motivation is.
16,000 DEC $21 PUT options traded at $0.72 = $1,152,000.
32,000 DEC $18 PUT options traded at $0.23 = $736,000.
Difference = $416,000.
The break even point for this would be $19.83 (using intrinsic value) if held to expiration if the article analysis is correct. It would be a bet on a sub-$20 close in Dec.
Could it also be insurance where they plan on holding the position through next Tuesday and the selling the $21 puts (if good earnings) and letting the $18 expire and pocket the $736k.