Yes, but that only puts an upper limit on the price that anyone would be willing to pay.
It's like this: Both companies estimate how much money they expect to make from using those servers for their own purposes. In Mistral's case, that might be a negative amount. Regardless, Microsoft obviously can put the capacity to better use. So they can offer to rent it from Mistral for more than Mistral believes it can make on its own. Basically, MS passes on some of their profits to Mistral.

The EU's AI Act calls them open source, so that ship has sailed.