I can't see any evidence to support what you are saying. XEM is open source. Of course, private companies can build on an open source blockchain.
Regarding the developer Makoto Takemiya, I can't say that I have met him. But I strongly recommend looking him up, watching a video and determining for yourself how much you would believe what he says, as much of the dispute between NEM and Makoto comes down to who you choose to believe.
Like many people, I fall way short of understanding the tech in crypto, so I put more weight on looking at the team, what they have done in the past, and how they speak and behave.
NEM has posted their side of the story here: https://blog.nem.io/makoto-takemiya-our-clarification/
The Asian bank you refer to is the National Bank of Cambodia. I couldn't find any announcement from the bank about their agreement with Soramitsu. Makoto announced it himself. It is also not at all clear how significant it is, as details are sketchy.
All crypto is high risk, so I am not recommended one thing or another. I appreciate your post, because anything that challenges assumptions in crypto is useful. It is all too easy to jump in head first when getting excited by a coin.