He felt “bad” for Chase, and to sum it up he lied about him sleeping with a dog bc he thought it would ease Chase’s mind to think he slept with a dog instead of being injected with rut injection (basically for extreme dominants they either need to have sex or get injected so the pheromones doesn’t accumilate in the brain and causes them to be brain dead or somthin)
It was actually explained in Kiss me if you can.
Chase doesn't want to sleep with anyone without feelings. So he tends to let his pheromones build up.
When his first rut hit Grayson panicked and got his dog, since there was no one around who could help. You need to understand how dangerous not releasing pheromones is for dominant alphas, and it's extremely important for their father Ashley. Ashley lost his ability to feel emotions and is dependent on his partner Koi.
But Chase passed out and they gave him an injection. The injection makes sense when you find out in Desire that Ashley found them when he got home.

Did the story ever tell the reason why Greyson forced a dog onto Chase while he was in heat . I forgot