Nope, sorry, you've met your weekly quote of contributing new and interesting things to the game! Your questions have been noted, rejected, and forgotten to the abyss.

If you really want to know, though, they are absolutely free to test out everything available to them to figure out that it's unnatural! There will be a few major clues as to it's wrongness:

1. The first is the obvious: it is completely obsidian in colour and splinters off in unnaturally jagged and sharp edges. This is generally not the behaviour of proper ice, and the natives will tell the Travellers there is no other ice anywhere in Yggdrasil similar to it if asked.
2. Though it is not cold by temperature, it still gives mild to severe frostbite almost immediately upon touching it with bare skin, and that frostbite is impervious to magical effects. This is, again, unlike natural ice and may be big sign that something in its essence is almost poisonous.
3. Fire and Ice Magic thrown against it will show absolutely no effect on it whatsoever. It'll be like it just glances right off of the wall, as though it can't even touch it.
4. Anything strong enough to mine diamond will actually make a kink in the wall! But it will be very, very slow going, and even if a dozen people were to keep at it night and day for a week, it would seem like they're getting nowhere - because they aren't! The ice continues to swell and grow every time it's lessened, like fighting back an illness that just spreads to a new location. Chip a piece off, and three new crystals will grow in its place.
5. The biggest perhaps most important clue, however, is that this ice is not just similar to the ice from Bad Moon Rising. It's exactly the same, and back then, it was produced by Travellers being corrupted to their cores and their connection to the gods being masked by that darkness. Anyone that experienced that corrupt ice will be able to tell you that it didn't come from having Ice Magic; it came from the corruption itself, and they could only manipulate it while they were corrupted.

Just a few fun facts about the ice! The Travellers can discover this information by playing with it and asking around, so it'll take some effort but it's all available for discovery. From that point, though, it's up to them to decide what to do with this information. We have a few ideas ourselves but we're trying to leave it up to you lot to toss up some suggestions for what the ice is and how to deal with it. If you think you've got something at any point in time, let us know! We'll work with you on carving it into something usable.