Known acids aren't supposed to eat so viciously through even metals, either, but whatever this type is does so with alarming speed.
Bishop identified it as "molecular acid", after studying it. There's room to potentially claim that might have been some sort of euphamism or informal term, for reasons of easy discussion between the group, but even if it's actual acid, there's nothing to say it might not also be somehow interlaced with other chemicals, to create the sort of violent reactions we so often view.
Note how Gedimen and Wren were so enthusiastic about study giving rise to "new alloys", medical discoveries and so on. These particular creatures are obviously way in advance of even their scientific thinking, let alone that of our own present time.
I'd imagine they're the biological version of the Terminator microchip and arm given to Cyberdyne: "It took us in new directions - things we would've never
When you think about the scene with the turrets in Aliens, think of how the entire walkwalk to the guns would be pretty much gone.
We already see that actual exploded aliens (or at the very least, a single heavily injured one) did melt through massive sections of the colony.