Oh yes, I’ve noticed that. And I believe this goes to prove how Stiles and Derek are loyal to each other and keep each other’s secrets.
We know Stiles had figured out about Kate and Derek’s relationship. He lets that slip to Derek in 3x10 at the hospital when Jennifer got away, but in 4x02 we find out that he hasn’t told Scott about it. He is shocked when learning it from Peter.
I think the same goes for Derek. I think he knows, or suspects that Stiles is something more than just human. And he’s keeping it to himself.
- Remember in 2x09 when Stiles’ stretches the mountain ash and activates it - Derek arrives right after and finds out stiles has succeeded. He might not have seen him stretch it, but he did see him break the line without touching it.
- Stiles did hold him up for 2 hours in a pool of water when Derek was paralyzed which is pretty incredible for a 16 year old.
- When Derek and Stiles was both paralyzed by kanima poision Derek was trying to kickstart the healing process to push the poision out. Stiles asks if it’s working and Derek says yes, i can feel my toes. Stiles looks 100 % done and says - dude, i can feel my toes. Derek looks startled - how could a human be pushing out the posion just as fast as him?
- And remember Derek insisted Stiles stay back and hold down Scott when he was going to help him with the tattoo using the blowtorch - did Derek know Stiles would manage to hold down a werewolf? or was it a test.
- He also saw Stiles bash a baseball bat against the merged voltron twin and it splintered completely. That takes a lot of force to accomplish.
There might be more examples, but you get the gist. Derek is much more observant than scott, and seems to have picked up on this. I think he’s protecting Stiles by downplaying it, what he can do, drawing attention away from him. They have come to trust each other, and this is Derek doing his bit to make sure Stiles is okay. I don’t think Stiles was fully aware of what he can do until recently either, and if that is the case, Derek has been very respectful of Stiles and letting him discover it in his own time while doing his best to keep it under wraps.
Aiden: So, you think he was just sleepwalking? Or is there something more to it?
Derek: In this town there’s always something more.
Aiden: What if I told you I know something more? I kind of overheard Well, I listened in on Stiles talking to Scott. How he thinks he was the one who wrote that message in the Chemistry room. The message telling Barrow to kill Kira.
Derek: You think Stiles, skinny, defenseless, Stiles is the Nogitsune? A powerful, dark spirit?
Aiden: I’m not the only one thinking it. I’m just the only one saying it.
Derek: This thing wants to possess someone and chooses Stiles? Why wouldn’t it take someone bigger, stronger? Someone with a little more ….. Power.
Derek is holding the spark plugs and trails off looking worried when saying the word power. I think it was stiles’ spark he was reminded off - and Derek knows or suspects stiles might be powerful.
The same goes for the conversations with Chris and Malia also. And notice that Stiles does the same as well - with the Calaveras in 4x01 most recently. As a contrast we get glimpses of their conversations with each other other implied conversations, and it’s clear that they’re not antagonistic anymore - they trust and respect each other, but still banter; so on the surface those not paying attention will still think of it as derek and stiles being the same jerks to each other as back in s1.