Assuming that panel b7 is mostly accurate. It suggests to me that there is a mirror-effect in play that explains the floor coloring, the scorch-mark, and Blackwing's position without any artist error involved.
For example, Blackwing could be leaving the dungeon in panel b7 and not still exploring the dungeon like everyone thinks he is.
However, the situation as a whole remains insufficiently explained.
Teleportation? Scrying? I don't know. All of that is speculative at best. Right now, the OotS seems to think that's what happened. But we know that even though there is a Conjuration effect and a Divination effect, but they don't have to be Teleportation and Scrying.
The real problem is Redcloak's True Seeing, which would cause Redcloak to notice "secret doors hidden by magic" as well as see "invisible creatures and objects" such as scrying sensors. If such magical effects were disguised with some sort of nondetection magic, then V's Detect Magic should've failed to detect them properly. This adds fuel to the fire of questions from the previous strip: there doesn't seem to be a clear answer yet to the question of why Redcloak failed to notice anything with True Seeing.
Redcloak notices the secret door hidden by magic (it doesn't matter what school of magic was used). There's no explanation for why Redcloak failed to noticed the secret entrance. It's a secret door hidden by magic!
If Teleported and Scrying, then Redcloak True Sees the invisible sensor.
Multi-dimensional stone! I foil all your spells - GM Hax - Ha ha ha? It's still the best explanation. Not that I blame a GM... I mean True Seeing: now I can't put any secret doors in my dungeons? *cry cry*