Saw this one late, but really felt I needed to chime in. FL4xe is right, that is a TT30 plug, specific for the RV world, 120V 30A. It is a 50A GFCI breaker. Here is the first concern I have. Is this wired in parallel for both outlets? Because if it is just a single outlet with a 50A feed, you can cause some serious damage before the breaker trips on overcurrent, since your plug is only rated for 30A. My guess is they cheated, and put a single 50A breaker in, and used one leg for one outlet, and the other leg for the other outlet, with a common neutral. However without seeing it, I couldn't confirm that.
they just connected the ground to the box and didn't use the ground terminal (you can see what looks like 3 total ground wires in the picture, none going to the actual terminal), which is pretty crappy, but not illegal, since by code you are not supposed to put two wires on one screw terminal of different core sizes.
Long story longer, I think everything to the breaker is fine (if you fix the ground screw connection) and you can put a NEMA 14-50 plug in. You would need to ensure the wire core size can handle 50 Amp for the run length (I'd probably use 6 gauge myself up to about 80', but I oversize everything
and the upstream breaker is rated at or below the components it is protecting, but that is it.
One more word of caution, many EVSE chargers do not like the GFCI setup. When I installed my level 2 charger, I cut the end off the charger and hardwired it so I did not need a GFCI. Most of the charger companies out there don't like selling hard wired ones because of liability, but there is no difference in the two, except for the plug on one end. Hope that helps.