I once chatted to a lady at a bike show about her selling paintings with motorcycle themes. The paintings were actual scenes of various events and dealerships but she would fudge out the Harley Davidson logos for fear of lawsuits.If he started selling them, I could see pushback (and it would be deserved). Making his own and posting it on a far away motorcycle forum is unlikely to get him heat.
In a court, I think the outcome of selling a work of art would come down to whether the buyers were purchasing the artwork for the skills and talent or for the HD image. I don't think HD had a chance of winning but the legal costs to fight the claim weren't worth the risk.
As far as the beach scene goes the argument would be how much would it have to vary to be "Inspired by" instead of a copy.