My fiance told me a female boxer puppy peed on Sandy when they're out for a walk. I was like

As usual, Sandy's sniffing and 'says hi' to other dogs, then came the boxer puppy on a leash. Sandy went to her, the boxer puppy started barking at him. Sandy was terrified and he immediately lie on the ground. Before my fiance could react, the boxer puppy peed on Sandy!

My poor baby!!!
Is it because he's small? Everyone's asking my fiance when they see Sandy if he's only 1kg (he's 1.5kg)... he's the smallest dog in our neighbourhood. There are other Yorkies but they're bigger.
I feel really bad for him.