That is incorrect. If the actions of Lincoln with regard to civil liberties during the war are to be examined critically, then so should the actions of his counterpart Davis. Failure to do so violates the "fairness" standard of ethical reasoning.
As usual, garbage_truck is full of garbage. Tu quoque, meaning roughly "you too," is a specific type of logical fallacy in which the arguer asserts that a noted wrong stated by a claimant to be dismissed, negated, or otherwise diminished due to an inconsistency, alleged or otherwise with other actions vis-a-vis the claimant or his/her claim.
The tu quoque fallacy is a variation upon genetic fallacies and fallacies of diversion in which the subject of an argument is reoriented or diverted onto a characteristic, alleged or otherwise, of the argument's participants and line of argument rather than the actual content of that argument itself. Therein lies the fallacy - it attempts to dismiss or diminish a noted point of argument without actually addressing or negating that argument per se.
In non-sequitur's case (a non-sequitur being another type of logical fallacy, btw) he attempted to diminish, dismiss, and/or negate the claimant's critiques of Abraham Lincoln's civil liberties abuses on the basis of an alleged inconsistency with the absence of a critique for Jefferson Davis over allegedly doing the same acts. As such, he committed a textbook case of the tu quoque fallacy, which, other than his namesake, is his favorite fallacy of indulgence. In this case, the fallacy is demonstrated by non-seq's attempt to divert attention away from Lincoln's asserted wrongdoings by calling upon what he perceives and alleges to be an equal and opposite wrongdoing on the part of Jefferson Davis who, though a comparable period figure, has no direct bearing upon whether or not Abraham Lincoln committed the wrong or the nature of that wrong.
In short, the Non-Sequitur, our resident Tu Quoque Parrot, squacked "tu quoque!" rather than addressing the critique of Lincoln posed before him. Therefore he avoided the argument.
As any rational man would believe.