Emoji are complicated, unicode has 256 characters called Variant Selectors (U+FE00U to U+FE0F and U+E0100 to U+E01EF), this allows you to change how an emoji looks, technically speaking, but like a lot of things in unicode, it can be "exploited" to do a lot of things, in this case Calle is encoding 965 bytes representing a cashu token in that emoji, you can copy paste it in most applications to send someone an emoji, that's actually a cashu token.

I'm currently not aware of any cashu wallets that support copy pasting the emoji to redeem the token, but it should be pretty easy to implement