All the Asian one I've seen also has it
They are in fact different Atomant. The USA version had to be approved by the ATF which brought about many changes to the design of the Asian version, specifically, the two notches/cuts on the two corners of the front of the magazine, allowing it to be inserted into a USA LM4. The magwell inside the ATF approved LM4 has two extra notches that line up with the notches/cuts on the front of the mag allowing it to be inserted. Real steel magazines, as well as the Asian version LM4's magazines do not have these cuts/notches, preventing them from being inserted into the lower receiver of the ATF approved (USA) LM4 PTR.
//sorry for odd autocorrect words by my phone//