It doesn't explain tokenizers well (or at all). There are better videos on the subject.

Anyway. Suppose you wanted to spell giraffe with the English alphabet in any arbitrary, phonetic way. You could also spell, for example; "jeeruff", or "djirough". You could count how many phonetically correct ways there are to spell "giraffe".

Tokenizers break a text into sequences of characters (even individual characters), called tokens. Different tokenizers use different tokens. The one they use here has "gira" as a token, but also "g", "i", "r", and "a". So you could tokenize the same text in different ways. They have a slide where they show the possibilities.