Your U.S. H\history class should have known that the Underground Railroad didn't end in the North, it ended in Canada. Runaway slaves in the North were still in danger of being caught and sent back under the requirements of the various fugitive slave acts. In Canada they weren't.
Since your history class wasn't aware of that fact then perhaps it's not surprising that their claims about what Lincoln believed in were so far off as well.
That may have been my forgetfulness on the Underground Railroad. You are right, it did end in Canada and actually a number of blacks settled in where my ancestors in Grey County, ON were in about the 1850s. My idea was that, if it is correct, many Northerners did not like blacks escaping the plantations to come up in to their areas and there was the school of thought that had abolishing slavery would put a stop to the escapes up north.