The story was written in the 1920s and the language has changed since then. "what he did" is an older British phrase that roughly means "this is what he did" often with emphasis, anger, or surprise depending on the tone of voice.

"Pooh was telling Piglet in a singing voice that it didn't seem to matter, if he didn't get any fatter, and he didn't think he was getting any fatter, what he did;" Ok - this on first reading makes no sense. However, if you apply the idea that commas can also give extra information , or asides, then we can (like a non-defining relative clause) delete them. So we get: Pooh was telling Piglet in a singing voice that it didn't seem to matter, {if he didn't get any fatter, and he didn't think he was getting any fatter,} what he did; (the middle comma is necessary as following an IF clause that precedes the RESULTANT CLAUSE) So the sentence's main idea is as follows... Pooh was telling Piglet in a singing voice that it didn't seem to matter what he did; I would say that this is poorly edited and should have been rewritten to make any sense!

I am an english speaker and this sentence sounds strange to me as well. I see there is a semicolon (;) used in the sentence which could shed some light on your question but never the less it still sounds strange. here is an explanation of the use of a semicolon: A semicolon is most commonly used to link (in a single sentence) two independent clauses that are closely related in thought. When a semicolon is used to join two or more ideas (parts) in a sentence, those ideas are then given equal position or rank.

are you sure you typed it out right what he did or is it saying which he did

ahh okay that explains it American English and Queens English. Good to know