Don't discount the possibility that thay had been sailing but for whatever reason went to motor only. There are times when I switch to motor because I'm close to my destination and found a convenient time to strike the sails. As I motor by others sailing I often think they're looking at me like I'm nuts. Even had one guy comment on the VHF. Had he be with me 20 mins earlier he wouldn't have made the comment.
Sounds like that was rust on the vhf. You didn't find any egg stains on your boat did you?