Could be. I had a leak similar to yours, only when it sat in a pouring rain though. Didnt find out till i tossed the headliner, that pretty much all my roof rack bolts leaked, but the rears were the worst offenders.
I put sealant of all kinds in the holes, on the bolts, and all around the bolts and the roof on the inside. Stopped the leaks in the rear and the fronts mostly, but all the others still leak. The only one that dont leak, is the one that is missing completely, that PO must have removed the bolt and the screw boss completely, and sealed it with something. Just wish i knew what it was.