There are three ways it could land, yes, but not all three possibilities are equally likely. It's more like a 49.999% chance of landing on each side and a 0.002 chance of landing on the edge (and that's being extremely generous).

Also true, due to surface area and weight of the coin and many other variables. But long story short, Xur is not RNG because Bungie placed him in the game to sell certain stuff at certain times in which they have decided.

Yeah, but the mechanism that determines which item to sell out of that predetermined list at that predetermined time is a random number generator. That fact doesn't change just because one item has more numbers that satisfy the algorithm's if:then requirements than others. RNG doesn't mean pure randomness, it means random number generator.

Right, but something being part of an algorithm isn't "random." The "RNG" system seems random to the player, but to Bungie it has a purpose. They have created said algorithm to drop different items based on many different variables, which we as the player will never truly understand. Which is why everything in the game seems so random. And Bungie has stated that Xur is in place for those who aren't "favored by RNG" (which is me).