Yes, it is. Good thing that's not what Durkon is doing.
It is not a "preconception" that Malack was in the middle of draining Belkar's blood by force, or that Malack just admitted to benefiting from the executions that he himself helped put into place. And as I mentioned in the main discussion thread, Durkon is not JUST reacting to Malack's vampirism here; a few strips ago, he was willing to argue with Haley that Malack couldn't possibly team up with Nale to seize the Gate—a belief he has just had disproven.
If Durkon had been sitting in Malack's study drinking tea with him, recognized what was in it, and jumped up and yelled, "Yer a vampire! I must kill ye!" then that would be racism, because there would be no evidence that Malack was at all a threat to anyone, anywhere. That is not what is happening in this scene.
Malack does not know Belkar at all. He does not know that Belkar is not innocent, and Durkon knows that Malack does not know.