I was quite confused too. I thought these were Pikaday implementations, partly because I usually use UK language in browsers, and then you get exclusively these (annoying to me) AM/PM date input pickers, and this time I didn't.
I tried some of the inputs and found that they worked well for initial input, but editing inputs didn't (e.g. the masked date input cursor just jumps over previous decimals, when typing a new number)
I made a reproduction video and tried to report it to the Pikaday issue tracker after which I found out it's deprecated.
Going back, and comparing the readme with the page, does show that the post uses native inputs. ... I feel that could have been more explicit; in this post I expected Pikaday to have the option to use native pickers with some component styling.