Yeah, I really don't see the ACD in him, either physically or with regards to temperament. I know the owner of his littermate said she could see ACD as a possibility; I think she has a bit of a sharper temperament, and she's built fairly differently. Maybe those genes just passed over Gusto. The person who originally pulled the litter apparently did see the dam, which I hadn't realized; she said she looked like a small, very freckled BC. But who knows, maybe some cattle dog behind that?
I still think the reality is a higher percentage of BC and that the "unknowns" must include some small terrier like creature - JRT/Rat/Boston. But I believe Am Staff (or some version of 'pit bull') and obviously the BC, and I'd buy that there's some ACD there (just maybe less than 25%). There definitely wasn't anything included that was completely off the wall, like Poodle or GSD or something, so I'm moderately impressed.