I've been a chef for 10 years, and I can tell you that if you want a proper result, you pre-heat the oven.
I am not targeting the woman in the video, more the channel itself, since I find it uninformative and just plain wrong to do it like she does in the video. They shouldn't have uploaded it in the first place, since half of this is bad technique.
Of course cooking is meant to be fun, and I love cooking myself, but it gets way more fun if you:
1. Practice your knifeskills to a decent degree
2. Use good techniques
3. Do it with friends.
If anyone thinks I am posting the message above, because she is a woman, I want to address that. I've worked with many very talented female chefs, who were just as good as their male collegues, if not better.