Nisuch is when a Nochri has intent to pour wine for Avodah Zarah. Shichshuch is also a common way for a Nochri to shake wine in a manner of pouring for Avodah Zarah. While Nisuch strongly implies pouring wine for Avodah Zarah, Shichshuch is only possibly a way to use wine for Avodah Zarah. The words "Morik Oruki" imply that the Nochri is merely doing the everyday act of pouring from one vessel into another. If he knows that this is wine and is pouring with this intent, the wine indeed cannot be drunk, and it is very similar to Nisuch and Shichshuch (how similar is discussed in the Rishonim). If he does not know it is wine, or mistakenly knocks it over so that it pours into another vessel, it is permitted. Our Gemara's context is that he is merely pouring from one vessel to another, meaning that he has no intent to pour wine, and it is therefore permitted. This is why it uses the words "Morik Oruki."

All the best,

Yaakov Montrose