If a bitch and a dog share the same dad but have different mums, and these two are bred does this class as interbreeding?

Any advice would be appreciated.  Thanks

This would to most people be classed as inbreeding, some would call it linebreeeding considering only full siblings and parent and offspring inbreeding, it is a question of degree, and opinion.

Interbreeding is normally the breeding of different lines breeds.

If the sirte were an outstanding dog and of proven excellent health and producing the same then a half sibling mating would be an advantage if the aim was to have puppies with the same percentage of his blood as the parents used.  It would also be a method of checking which traits were most likely passed on by him, good or bad.