Yes, you are right. Its our fault. The source of text should be mentioned in our document.
You should be more careful before making a whitepaper, if you want to be serious in this matter, you need to do it professionally, don't just copy and paste, we know that current projects often make mistakes from their whitepapers, therefore the source is very important if you want. use that content.
There have been many WPs that I found before, the beginning is the same as yours, even all of them were copied without explaining where the source came from.
I personally think that the essence of plagiarizing is causing it to appear that you were the one who originally created such thread, but in fact, you stole/copied it from a different source.
Even if the whitepaper contained sources, but if you copy-pasted without even changing a single word/phrase from where you got the information constitutes plagiarism. Posting the link and indicating the source on where you copy-pasted the information cannot remedy the fact that you made it appear that you were the one who made such statements.