In this case the LLMs are just coding (or attempting to code) a clock with html and css, possibly javascript too but you wouldn't necessarily need it. Part of the prompt was leaked in this other comment: https://lemmygrad.ml/post/10677257/7733548. Then the website grabs the LLM's answer and displays it. So the LLM is not generating the clock directly, it's just writing code that you then run.

As for how it generates uhh

(no more precisely they tokenize words, breaking them into a unit the neural network can work with, then they also transform words into tensors, which are arrays of vectors in N dimensions, which gives each word the LLM learns semantic closeness between words and concepts, then after that the rock we trick into thinking performs magic and outputs a sentence).