I agree in so far as it seems class-specific uniques have an ungodly higher drop rate. I saw the sorc ice pants drop 4-5 times in succession without another unique myself.
It could always simply be a matter of statistics; with so few options to drop that seeing the same one in succession isn’t all too rare. It could also be a matter of specific area having a higher drop rate of certain items. i.e. if you’re spamming a single dungeon and that dungeon has increased chance to drop specific items, you would of course expect to see them more.