I, too, would bet it was an old, well-educated bear that picked up your scent. They don't get old and big by being stupid! Also agree on acorns keeping him from your bait set up. Also recommend you try still hunting the oak groves. I would not bet on it coming back to your bait this fall--when we've busted really big bears off bait sets, they just disappeared from the area. Smaller ones were still around, but not 'grand daddy'.
Best of luck, Arch