This is another one of those parson's specific problems that's really common.
My personal opinion is that it's an infection, but localized and not overly aggressive, like gingivitis. These guys have really soft skin, and are not very tolerant to any kind of bacteria loads so any little scrape or abrasion, stuck food etc. on the lips can start developing these marks.
Both sides of the mouth in the same place is the most common location, that's where the insect gets crushed against the lips when they chew. Usually it doesn't progress past this stage, but they can develop stomatitis that involves the gums, teeth and jaw so it's a good idea to stay on top of it. I've been able to completely cure this by brushing their lips twice daily with a very soft toothbrush and betadine. Look for any stuck skin or flaps that move when you brush, a lot of times these are encapsulated and need to be debrided a bit. Don't be afraid if they bleed a little, normal. It takes a few weeks of this routine, these guys are really slow healers.
I'm not sure if there's a way to completely prevent this, I think feeder cleanliness and overall health is much more important in prevention than hard shells or leg spines on insects. I never bother removing parts of bugs before feeding and almost never see this in my own animals. I "have" seen this consistently with animals that came to me from someone else, so they must have been doing something differently, or they weren't kept in ideal conditions (parsonii margin of error is about +/-5%)

Your guy looks great otherwise, I don't think this requires a vet visit.
I would double check the inside of the mouth for any redness or sores just to be safe.