I found that dog on the street

That's Otto, I found him on the streets. He seems to be a mix of breeds, but there are a few things that's standing out for me. He acts like a border collie. I had border collies and other breeds before. And he acts just like them. I also asked the vet nd he also thinks he's a collie mix, but I wanted some other opinions. He's extremely smart, in two weeks I taught a lot of basic commands. He's extremely active and only wants to stay by our feets, even at night he won't left my side during sleep, only when he hears something strange, but then he comes immediately back.