yeah, that's probably not really aggression, it's HEELING. The dogs are bred to herd cattle by nipping at their hind ends. Out of control heeling, no good, but not really aggression.
I've met a couple of heeler/Aussie type dogs who were bitey. One was, I think, a fear biter but in a really bad way. It lived at a public stable and actually came out of a crate/doghouse in the barn aisle to bite a kid in the leg as the kid walked past. Absolutely unprovoked, kid didn't even know the dog was there, in fact I didn't either and I was standing right there and had been walking around that barn the whole day. Very weird.