It might help if you say where you have read that, because either your source is incorrect or you have misinterpreted it. The node definitely works without having armour.
Armour is a flat number that is used to calculate damage reduction of physical hits. I think the problem here maybe comes from understanding that or your character sheet. The percentage it shows on your sheet is an approximation of how much damage reduction you will be getting from armour.
So with 0 armour the sheet will say 0%. When you take that node you will still have 0 armour, but that percentage will rocket up to, for example, 62% and now you will be reducing the average physical hits by 62%, clearly a massive increase. The calculation to arrive at that percentage went from using just armour (0) to using armour + 60% of es (0+6,000 for example).
Hopefully that makes sense!