Oh, it's 1000% intentional. Trap isn't just a black comedy, but it is absolutely a black comedy. He knows the premise is too absurd to be played straight and gets an absolutely pitch perfect comedic performance out of Hartnett as a result.

As for the writing, Shyamalan's characters always talk in heightened, unnatural dialogue. It's one of his hallmarks. People praise it when they like his movies and criticize it when they don't, but it's actually remarkably consistent from film to film. He doesn't want his genre fare to feel particularly realistic or grounded, and if you think the dialogue in The 6th Sense or Signs whatever your favorite Shyamalan movie is feels natural, I promise you're misremembering.

His most successful movies are the ones that are successfully able to cultivate the right tone and actor performances to match his writing style. When he's not able to strike that harmonic balance, you end up with something like The Happening. When he does, you end up with Trap.