Confused doggy :0)

At puppy socialisation this morning there was a small black poodle x ? it was presenting to a male Mastiff x They were both around 8-9 months old, the Oodle was really shoveing it's back end into the Mastiff's face and moving it's tail to the side

I I mentioned it to the trainer and he said the Oodle was a male too We spoke to the owner and it was a rescue and had been castrated around 6 months old and evidently the dog presented itself to all male dogs

Why would a male do that to another male? Could it have something to do with early castration? Is it a submissive thing? Or does it simply prefer the attention of males