It's meant to be vague. He's threatening Chase. Have read the book so let me know if you want a spoiler.
Mind dropping the spoiler? I’m impatient
spoiler
Grayson told chase that he spent his first rut with a dog, instead of spending it with josh. thats why hes so afraid of dogs
Spoiler....
His brother is an absolute arsehole. Chase goes into rut due to excessive pheromones (alphas are practically delirious when this happens) as Chase is a Virgin, no hoe this man there's been a build up. So turns out he actually spent the rut with Josh but has no memory of it (this is when he marks Josh and gets him pregnant) but his brother convinces him he did it with a dog. Chase is a sensitive soul who loves animals but his family are psychos so saw this as a weakness and this was one way of psychologically torturing the poor guy. This is also the backstop as to why he's an arsehile and refused to let dogs be part of his security.
Wait! What did his brother tell him that made him go to the party? I didn't quite understand the translation! He mentioned a dog and stuff but I didn't get it...