... yes, that is literally Stiles' inner keysmash-monologue upon seeing Morgana's writing. Because Morgana means Arthur's sister means the witch who Merlin hates and who got 947889373985 people killed and also she's evil.
Except obviously she's... pre-evil. On the way to evilness? Not yet Darth Morgana but a sith-lady-in-training?? Same as Anakin in Episode 2? Yeah, that's an analogy that works.
... now if only that helped him figure out what the hell to say to her.]
Fh-glubrlg? [The answer, apparently, is incoherent gibberish that the journal records him saying, completely and utterly out loud, because right now, Stiles-always-has-a-smart-remark, is also completely and utterly out of words.]