This Moonstone Bank situation sounds incredibly similar to Full Tilt's attempt to buy SunFirst Bank in St. George, Utah. The plan was to use SunFirst to quietly process payments and list them as something other than gambling.
Eventually it became a $10 million investment in the bank by Full Tilt via payment processors Chad Elie and Jeremy Johnson, in exchange for processing online gambling transactions. This eventually led to the collapse of Full Tilt, as the FDIC ordered SunFirst to stop processing these poker payments in December 2010, thus leaving Full Tilt without a processor.
https://archive.sltrib.com/article.php?id=51636750
I'm guessing that SBF needed a US-based bank to help him to shady things without asking questions, so he infused $11.5m into a tiny bank in Washington, with the agreement that they look the other way.