Really, what does Sacch do that increases sour? Can I add some lactic bacteria later if it's not sour enough? And how come one of my local brewpubs (The Alchemist in Waterbury) makes some all Brett Beers and they're sour? Are they perhaps adding bacteria?
Sacch increases funk, not necessarily sour. Greg Doss from Wyeast gave a talk on this at the NHC a few years back, but the gist of it is that the sacch creates precursors that the brett can convert into compounds that give the distinct brett taste.
Some people say you can't add lacto after the fact, but i haven't tried it by itself. Cascade Barrel House in Portland adds lacto after primary with sacch and gets some awesome sours beers, but they aren't using brett at all. Lacto converts sugars to lactic acid, so if the brett has already chewed through all of the sugars then the impact from the lacto may be minimal.
The place near you - if the say they are doing 100% brett then I'd believe them. Different things can cause sourness, not just the brett. But also different conditions for the brett can cause different levels of acetic acid production. And there are probably strain to strain differences as well - do you know what they use?