I wouldn’t think twice about it. First thing is that he may not even know how serious it is so you would be doing him a service by informing him. It is our job as Part 107 pilots to teach and train, not just act like you are better than everyone who doesn’t have their license. I think the pilots that act this way need to be put into their place. I have no problem confront a Part 107 pilot if I see them doing something dangerous, particularly when it includes people or property.
Secondly it is that we are ethically bound to protect the airspace that we use so it is beyond legality at that point. Also, did you put in work to get your license? I did. If someone is flying commercially and doesn’t get their license because of laziness or fear then that person shouldn’t be flying anyway.
As for the fines, those are the maximum limits. Standard fines to this point are in the $1500-5500 range. There have been some larger exceptions, but you’d have to be pretty ignorant to get one of those.