Yes. I just said. IOs often make mistakes at the airport. I once came in on an OA visa and got stamped in for 90 days. I checked the date and pointed out that the stamp should be for a year. The IO acknowledged his mistake, voided the stamp, and stamped a new one for a year. Mistakes happen on both sides.
According to this infographic on the Myanmar Embassy website, Myanmar citizens can get the 45 day visa exemption, which sounds the easiest way to enter