We also have a 34.4, 2016, but it DOES have a locking latch. I wonder if this is a manufacturer error. I suggest calling Thor and having them send you a replacement.
You can adjust the catch on the motorhome. If the door popped open, a locking latch would not prevent this. Evidently the torque of the RV as you began to move caused the latch to release from the catch. You can loosen the 2 screws holding the catch in place and slide the catch as necessary to tighten the latching mechanism.
As a side note, I always walk around my coach and push each latch to make sure it is fully engaged, as my final step before taking off anywhere.