There are a lot of factors that could have led to the increased acidity, but generally speaking, throwing spontaneous dregs (such as JK, Allagash, De Garde, and any true lambic) is a YOLO, especially only 3 days in. Don't get me wrong, my best beers have used dregs, but I don't go into them expecting to recreate that beer. Throwing LAB at higher pH wort with lots of fermentable sugars has a lot of metabolic paths to add acidity. Some brett strains even produce a genuine tartness, and don't care about your IBUs. I have one brett strain I co-pitch with Sacch in primary, it routinely gets the beer down to 3.7pH in 4 weeks. Hell, even some sacch strains can finish quite tart, and now Lallemand has their
sourvisiae.
Like RPh said, if you want saison phenols like the classic 4vg (clove, spice), you should delay pitching a culture like MFB. You can also ramp up the heat, underpitch, do other things to stress the yeast out, but this can lead to mixed results. Pitching from a new packet I get some phenols early on and the brett is somewhat mild, and stonefruity. But compared to using Dupont then Orval strains / dregs, I get a much more phenolic beer. Bottom line, pitching such diverse dregs that early on means you have gone completely offroad, and there is no real map other than the one you chart for yourself.