Then I wouldn't be concerned personally that they put a construction joint below the wall. Generally though, I tend not to have my slab on grade rest directly on the footing and it tends to cause cracks in the slab at the edges of the footing. I typically have two possible details, 1) top of footing is top of slab and there is a construction joint at the transition between footing and slab, 2) if footing bearing is some distance down from slab elevation I'll pour a curb from the footing up to the top of slab and have the wall rest on that. Both details do not have the slab run under the wall.