probably cause he's always in the way
LOL
Just like He Tian thought about Mo when he dreamt about the puppy .... Mo thinks about He Tian when he sees a puppy. I think it's not about appearances but about seeing each other as a puppy of some kind that needs someone looking up for them.
Remember that from Mo's point of view He Tian can't even feed himself properly and always needs his help ( he doesn't know He Tian call him up to clean and work mostly because he just want to be with him. To Mo, He Tian is like a puppy that can't take care of himself).
How does that dog even resemble he tian?? Wtf