I don't even understand the comparison. They were buying (not selling) Bitcoins directly from sellers. Western Union is specifically engaged in the business of enabling people to send money to others.
They were taking money from customers, in exchange for which the customer received some sort of token of value, which could be used as a medium for exchange or reconverted to USD later.
It's not a token or store of value. Bitcoins only have value to the extent that others will buy them. There is not a person on the planet that has a contractual obligation to exchange or buy Bitcoins for anything.
You're right, we are literally talking about the buying and selling of random numbers. However, once again, Bitcoins have zero inherent value. There is no person or organization that has any obligation to buy or otherwise exchange them. They only have value to the extent that others will buy them.