I don't know what software this is using, but that could be the history software considering entire edits as single deltas. Editors using CRDT or OT will commonly compress deltas like this.

could be a byproduct of the algo that's recording what he types. Instead of saving the timestamp of each keystroke, it does "every 500ms, save all the characters that have been typed in the last 500ms" or something like that.

To be clear, this is speculation. I haven't actually looked at the code that creates the recording. Just pointing out that the process of recording often alters the recording itself.