Here's the full story. In my 20 years of playing at the club I belong to, I've never come close to calling a penalty on an opponent in a tournament - and I've participated in many tournaments each year. In fact, quite the opposite, if I saw something unintentional like a partner touching the putting line instead of hovering the club above it, I would wait until after the hole was over and explain it to the opponent so they'd know not to do it in the future.
In the case of the rule discussion above, I was playing in the Finals of a Member - Member event and our opponent did what was described above. To be honest, I've never seen something that blatant before and I felt it was something that created an advantage, so I mentioned it to the pro who was monitoring our match and he asked the player. They decided it wasn't a penalty - the pro said it wasn't in his through line. I was almost certain it was a penalty, but just let it go without comment. We ended up winning that hole, so it had no effect.
The opponent however was completely pissed at me and still is and said he thought it was customary to fix things like that. I didn't argue his point despite rarely if ever seeing anyone fix anything in a fairway except for filling an unfilled divot - and certainly never seeing anyone fix anything close to their ball. Just wanted to see what people on hear thought about the situation.
We ended up losing the match in extra holes (21) in large part due to a 1 1/2 foot putt that I missed (choked) on 17. Played well overall, but it'll be a long time before I get over that putt.