Individual IP addresses are re-used and assigned randomly at MacStadium. If you are a new customer and the IP address for a server you've rented has a hostname on it, then the previous user of that IP address may have manually requested a PTR record added to that IP address. This is rare, but still a possibility.
PTR records are a complimentary, manual service we offer to customers. If you receive a server with an IP address that has an existing hostname, please get in touch with us via support ticket to have it removed or replaced if necessary.