No they weren't, and I challenge you to show any source calling Mongols "Orcs" prior to the LOTR books. The closest you'll come is Tolkien (who based the word on an old Anglo-Saxon word for goblin) writing in a letter in the 1950s that orcs are “squat, broad, flat-nosed, sallow-skinned, with wide mouths and slant eyes: in fact degraded and repulsive versions of the (to Europeans) least lovely Mongol-types.”
Now it is true that Mongols have picked up the term themselves since the movies, using it to basically call a fellow Mongol a redneck.
I wasn’t going to bother to reply, but you might find it interesting in this and other regards:
I actually read one complete reference of many that specifically said ‘Orc’ derived from some other non-English, or non-modern English word like ‘Orciag’ in reference to what the Mongols were called in the 13th century, including the complete etymology.
But, it seems in this day and age with proper pronouns, calls of racism at every turn, and other woke word fetishes, the page has been scrubbed.
The only way to learn about this term in association with Mongols is to visit a big university library that has not been purged as well. Other stuff like this which was easily available on the web is also likely purged as the woke snowflakes rewrite history and the dictionary to their satisfaction by removing everything they consider ‘offensive’.