Battery charger likely puts out 30A into the batteries and pulls 3 or 4 amps off of the 120V to get that done. The rest of the trailer (powered down) is well under 1A. So - was the fridge on? How about the water heater? Both can pull a bit of current. Water heater will probably go over 10A with the new system.
Assuming we're talking about the P3000, it's a 2600W generator. On that basis, 100% would be 21A. I have no idea how they do the indicator so there is an assumption there. 47% would come in at about 10A, so water heater + charger + fridge could easily get there. They also could hit the 47% point if the 100% mark is 3000W ( = 25A).
Yes, this does make you wonder just how a 30A trailer gets by on the power available. To some extent the answer is that not all 30A breakers trip right at 30A