It's just a link shortener, but using Emoji instead of alphabetical characters. Nothing prevents you from using non-conventional digits for some number base. If I want to, I could make "abcdefghij" be the digits for zero through nine in base ten.

If the domain is what surprises you, that's not new. Internationalised Domain Names have been around for a while now, and support any Unicode character (with registrar restrictions to prevent phishing etc.)