This may be viewed an impolite way of addressing Pup Ears, as Souta doesn't know him.
It's like saying 'that dog guy'. But, in Sakana-rin's view, read below.

This is how Souta refers to Ears Pup, like a brother! So, he's heard of Kagome's tales and likes him, perhaps.
The poor kid saw the well open, and something reach out to take Kagome while he was near wetting himself.
It was traumatic for him, and next thing he knows she came back in miko clothes.
He must've asked Kagome what happened, and she would come to talk about an arrogant, selfish boy...
Souta would know that Inuyasha is strong- what with the boy sonic-spinning through Centipede Woman and the like.
I wonder if Kagome told Souta of the pup's ears.
 I mean, maybe he knows as she must've described him in some way for him to know the 'Inu' [dog] part.
 With the boy's recent resistance to letting Kagome go home,
he must've got word from Kagome's perspective of him being rude.
Remember, Inuyasha has spunk, grit, and determination to get that cursed jewel; shards and all.
Remember back in episode one, Kikyou called out 'Inuyasha'?
They've met something fierce before. Ooh, ooh.