Thinking about what Charlie must know with what he has.
He knows, (like all the other sides, pg 138, panel 6 onwards) that when the multihex dirtamancy trap set-off, he lost all his units that were in that sphere. As in, they were croaked.
Then, he sees that his units again, units that he is aware he lost in GK, (as he knows them by name he would know which ones specifically burned to the ground) when flying too close to Wanda's strike force.
Assuming he has a visual on them, (as he recognised them, or was relayed what they looked like) this would seem very odd to him, as they would not have appeared uncroaked, but in "that black rainment"
So, what would he think from here?
If they are uncroaked, it is not in its usual form. This has the implication of "what the heck is this new trick Parson has up his sleeve?"
So, from that point, he asked Parson.
Looking at this snippit:
CharlsNChrg:What were they doing in that black raiment, fighting for Gobwin Knob?
LordHamster: If you read that question again, Charlie, you'll notice that it answers itself.
CharlsNChrg: You know what I mean.
I took Charlie's last comment to mean, he was more asking, "What were they doing alive and well and fighting for GK, no less?"
In short, Charlie has no idea what this form of Croakamancy is, (as the uncroaked Archon and the decrypted Archon look very different) or where it came from.
Ways he could figure it out? Ask Jetstone. They must have records of how the Arkenpliers fell into their hands to begin with. Maybe something in there said about the Decrypt effect. At the very least, he would discover they do not hold the Arkenpliers anymore, an artifact he was seeking. From there, he may put the theroy together that the Pliers which are an effective uncroaked weapon and this new type of Croakamancy may be related.
Edit: Charlie also knew that the pliers were at GK, so he might not even have to think that hard, if he knew their unattuned ability. If he did not, then it is back to asking Jetstone.