If you follow the thread starting from the quoted tweet, you will read the statement “you can’t even pass real props down”, and that’s false. So I assume that if someone writes something like this, it means that he doesn’t know how Custom Elements work. There is nothing wrong with this, but since there are a lot of misconceptions around WC, I just wanted to clarify how things are.
I agree that using attributes to pass all kind of data could be much more convenient but, as I wrote, this is how HTML works and everyone can build a little abstraction on top of that. Problem solved. :)