Yes, a Roman Catholic Mass and an Eastern Christian Byzantine rite Divine Liturgy are two different things. But in essence they can be viewed as different ritual expressions serving a similar purpose in both traditions, whether some Orthodox, so conditioned by anti-Papalism or some Roman Catholics, full of arguments about infallibility and the Pope, want to admit it or not.
While somewhat simplistic, this article outlines the differences and similarities between the Mass and the Divine Liturgy. "Comparison of the Roman Catholic Mass with the Eastern Orthodox Divine Liturgy" http://interchristianos.blogspot.com/2010/07/comparison-of-roman-catholic-mass-with.html
The author makes this observation, and I would argue that he is close to the point here, "it seems to me that the differences between the Roman and Byzantine liturgies is not theological at the most basic level (they both see the liturgy as a proclamation of God’s Word and as a reception of Christ’s body and blood made present on the altar), but rather a divergence, to some extent, of the focal metaphors for the liturgy. To phrase it differently, the different theological emphases of these two traditions are centered more on the why and how of the liturgy (i.e., its particular form) than the what of the liturgy (i.e., its essence)."