No, this is not a strip bashing Lincoln for being gay. I have no idea if he was or not (there are apparently some historians who believe so, or at least making money peddling theories). The ultimate “friend zoning” would be this relationship, but is in no way encouraging violence against gay people. It’s a joke.
This disclaimer is placed here not to defend ourselves against gay people (they usually have a splendid sense of humor), but to keep intolerant idiots from reading too shallowly into it.
TREY: Are you...?
LINCOLN: Abraham Lincoln? Yes, I'm afraid my homosexual advances were rebuffed by John Wilkes Booth.
LINCOLN: Are you upset to find out I'm gay?
TREY: No, I'm upset that this another awesome story about history my teacher never told me.