it's not as rare as people believe. People drop commissions, switch branches and do all sorts to get into SF or fly as warrants. I've seen SF Captains drop commission to stay operational on a team as a fox, after a hell of paperwork and training of course.
dude could have easily gotten out and joined the army.
Buddy of mine, former marine doing the same job on the marine side of the house did a branch change into the army. didn't have to attend basic or MOS training because he was already mos qualified by army standard. he literally wore marine camis one week and acu's the next. different people have different circumstances so unless you have specific facts that discredit this guy, stop questioning somebodies service.
this stolen valor shit we keep seeing on social media is starting to drive a wedge in between our brotherhood of being in the military. the first thing people think when talking to a former soldier nowadays is "how can i get this guy for stolen valor" and it shouldn't be this way. if he starts rambling off shit that, generally by assessment through common sense, doesn't add up at all, then sure be skeptical.
so, does it typically occur that a marine switches branch to become a green beret? no, not typically, can it? yes absolutely.
general guidelines to asses SOF.
if he says "i was SOF. he was probably a support element in SOF" if he says "i was a seal" and hasn't written a book about his last mission, he's probably lying if he says "i was a green beret" and doesn't have his green beret stick out of his cargo pocket about half way, he's probably lying if he says "i was 160th" he was probably a fueler in the 160th if he says "i was air force para rescue" got nothing, had no run ins with them yet. if he says "i was a ranger" and doesn't have a scroll somewhere on him, even in civilians, he was probably an s1 clerk who went to ranger school via reenlistment option. if he says "i was marsoc" and isn't eating your face at the same time, hes probably lying
also the guidelines are a joke, in case any of those safe space needing mofos are on here