About to mount a 86” (100 lb) TV but should I be worried that when drilling the pilot holes, the left stud offered much less resistance than the right stud?

I used a stud finder to narrow down the center of the 2x4’s which I’m very confident of. Both studs produced sawdust when drilling the pilot holes but the left stud didn’t offer too much resistance when drilling or screwing the lag bolts. The right stud on the other hand was tough to drill and tough to screw the lag bolts into. Should I be worried or what could be causing this? The tv mount is rated for 132 lbs. House was built in 2000.