As far as turning in the yellow quest first WHENEVER POSSIBLE, that is in situations where you would save time because after you turn in a yellow quest you will have access to new blue quests. This is first evident in the hub right outside of the first village. If you turn in the yellow quest before the blue one, when you do turn in the blue ones you can accept the new quests from the NPCs that have them right away.
If you first turned in the blue quests you would walk around and talk to all of them and turn the quests in, and then turn the yellow quest in. When you came outside you would have to talk to most of them again, therefore wasting time. Situations like this occur frequently during the level up process, and at any point you can save time by turning in the yellow quest first, it is recommended to do so.
The guide was a direct conversion of his videos, every step he did and the comments he made were all (mostly, not sure if typing everything he said is the brightest idea) translated into a readable text format. Also, there’s no need for the guide to prove anything, the videos are real time sped up 10x Blade & Soul Gold without any missing parts, and explicitly showing him reaching 45 in 15 hours give or take 10 minutes or so.
You or even me might not agree with his methods, and quite frankly I didn’t agree with some small parts of what he did. But I can’t deny that his method works. Take that as you will.
In regard to turning yellow quests first. I said before, the guide is very specific, which means even the quest order was quite specific, or at least as far as I’ve tried it. It’s not a general sense of turning in yellow quest first then blue during your normal questing, it’s turning this quest first then this one to make the guide works.