Maybe I'm projecting, but I don't see it as suspicious. It may not have been the wisest or most mature move on his part - taking the money out of the envelope, staging it in his bag and snapping a photo to send, but I don't believe it was anything but kidlike enthusiasm.
Granted, I haven't seen all his SM postings, but from what I did see, I didn't get the impression he was bragging. My thoughts were that he was a happy guy loving his work environment, and he has a sense of humor. His comments about his office smelling like leather etc. made me smile. It's young man stuff. Er, I guess it's guys-of-all-ages stuff

I dislike a braggart as much as the next person, but I honestly didn't get that. Sometimes, people like to share something out of the ordinary and I think that's what he was doing by sending it to his GF. It certainly would be novelty to me to have $40,000 cash in my lap and while I wouldn't open a package that I was supposed to deliver to my boss, I can absolutely see the attraction of doing so by this guy. I don't know the nature of the relationship of the three as boss/employee, but if all three were facebook friends, it would appear to be relaxed enough and trustful enough that JW posted those pics and comments and he wasn't fired. Fellow car enthusiasts and he had a great opportunity for so many things other than being a driver/PA for the rest of his career.
Sometimes, people like to share things when they can't believe their good fortune, or good luck in being fired from one job, but being hired by the big boss into a position of trust and some sort of intimacy that goes along with it. No weirdness intended.
I'm babbling, but I just think he was happy guy with a great boss and a great job from what we've seen.