[Do you ever think about how Merlin very deliberately kept Douxie out the loop in regards to the fact he was up and running again, right there in Arcadia no less, and that the Eternal Night was coming? He and Hex-Tech were completely caught off guard when it did happen shown by the fact he was not wearing his bracelet leaving him to protect the girls with what he had to hand instead, a clear favourite guitar that he would later match his staff with. This is also when he slipped up mentioning knowing of Gumm-Gumms prior though that would have meant nothing to Mary and Darci at the time. He would have recognised Morgana too if he caught sight of her because regardless of the what happened in the original timeline, he would have known her prior to the fall including the imprisonment plus her magic is very distinctive.
Douxie did what he was told and kept his head down, stayed out of troll politics and helped wherever he could while keeping tabs on things and when suddenly his own history came barrelling to the forefront he was still expected to step aside and do nothing. As a Guardian of the world, he fought back instead.
This guy was (Rightfully) so angry with Merlin when he finally popped up to address him in Wizards, that he took until that moment to get in contact despite having the ability to do so at any time to the point of physically in recent times but chose not to. He trusts Merlin, he really does, but he will have been second guessing if maybe he wasn't considered good enough to help.
From how he was treated prior to going back to the past sadly, that fear was likely reinforced in needing to prove himself no matter what the true intentions behind the why.]