I think outside of formal settings and in everyday life, it is common courtesy to give credit to people if you use their work or reference their ideas.
Correct, that is a copyright violation. Based on the links above Tasty's videos are neither plagiarism, which is an offense in academia, but not commerce, nor Copyright, the commercial equivalent, which does not protect recipes.
But do you understand that it's ethically wrong, regardless of whether or not it's illegal or formally defined? At a minimum, it's rude to copy someone's work without thanking them. You shouldn't need a higher authority to tell you this is wrong.
I'm not sure it's ethically wrong to take something in the public domain which holds no license or copyright whatsoever, and use it without attribution.
If snippets of the video were direct cuts from another show, that's a different story. But making a dish yourself and filming it is your own creation, I don't see why you have to thank anyone for it.
It is. It's benefiting from someone else's work without thanking them. This is basic elementary school ethics.
It's equivalent to performing a symphony, but not mentioning the music was written by Beethoven. Not illegal, but wrong, even if you don't explicitly claim it's your own work.
It's the same as calculating force equals mass times acceleration, without thanking Newton every time. That's an example (natural law) which is always and immediately public domain, the same as recipes.