I was thinking the same things like you. Looks like they don't event hide the actual message. They basically hide some sort of ID that points a row in the database. After some research I've made a web-app which can hide any message into any text.

If you wanna look it's on G⁡⁠⁢⁠⁠⁢⁠⁣⁠itHub. Here are the links.

Demo: https://ozgrozer.github.io/titus/

Source: https://github.com/ozgrozer/titus/