It's probably operating on UTF-8 data on a byte-per-byte level without any additional processing. Just feeding it the raw string data and letting it assign the tokens.

It's similar to how it is splitting words at arbitrary points, rather than at clear morphological or lexical locations (e.g. on the Jane Austen text `"Now, ma'am," said Jane to her aunt, "shall we join Mrs. Elton?"` I've seen it tokenize that as `"|Now|,| ma|'|am|,"| said| Jane| to| her| aunt|,| "|shall| we| join| Mrs|.| El|ton|?"`).