No, they are not the same. Open relationships are often just about fun with sex, spicing up a marriage, etc. While polyamory is about dedicated loving relationships that are more often committed and even fidelitous in many cases.
Polyamory comes in many different forms, and an open relationship is one of those forms. There are also different types of open relationships, some of which incude very loving and committed relationships.
Since there are closed poly relationships the terms are certainly not the same thing.