He's most likely referring to skills like the wl/r shadowstab, which deals magic damage through an elite. Against geared rogues, the rogue "resists" almost all the time, but against priests, the resist rate is nearly 0. The conclusion here is that the resist rate for a skill that does magical damage, but originally was physical damage, is getting dodged by the rogue, and on screen it appears as a resist.
In a similar manner, the m/s shot can be dodged, resulting in no damage taken. However, I have never seen it resisted. To prevent m/s shot damage, you use rainbow candy. Not quite the same as above, but another variation.
I understand skills like m/s shot and w/m k/m white attacks. The way those work is that the skill does white damage FIRST. If that white damage hits, magical damage will also be applied. I rather enjoy this mechanic. If you cake a m/s, they can hit you with shot and still hit you with magical damage. IF you candy them, you risk being fireballed, but shot will be blocked.
What i am confused about is the warlock skills. It sounds like the warlock skill is supposed to do outright magical damage, but can be dodged because its based on physical accuracy? If that is the case, is it really a glitch? Is it magical damage w/ physical accuracy, because other skills have that kind of feature. Shadow prison is non damage dealing, but is based on magical accuracy on a physical dps class.