They own some of their servers and rent others. From their FAQ:

All of our VPN servers are encrypted and are either owned by us or dedicated servers that we rent.

• Our rented servers are all dedicated, meaning they are not shared with anyone else. We do not use virtual servers.

• With the servers that we own, we have physical control over these, which means they tend to be faster and more secure.

When connecting, you can filter to only show owned servers.

Mullvad all the way