I hate to burst your bubble but this dog isn't a Tibetan Spaniel. Might he have some in him? Yeah. But they're fairly rare dogs, and I can't say I've heard of them being wildly popular in Italy. Along with that your dog is at least twice the size of a Tibetan.
Typically street dogs are multi-generational mutts like mathilda said. Personally I think your dog looks like he has some Golden Retriever in him that would account for his beautiful coat and some bully breed that would give him a blocky head and shorter snout.
This is a dog that would be interesting to do a DNA test on. But with street dogs you will sometimes get an untraceable result because they're so deeply mixed it's hard to pinpoint breeds.