He didn't say the Galaxy S3 and S4 were cheap low end phones, he said Samsung's market share in general was made up of cheap low end phones.
And that would be true assuming we're talking of worldwide market share.
U.S. market share is another story, and it's true that high-end Samsung phones (Galaxy S/Note lines) sell a lot more, but I doubt he'd even be defending Apple's US marketshare because he wouldn't need to. Apple sells significantly more smartphones than Samsung in the U.S., even including all Samsung ranges of phones.
There's a huge discrepancy in average selling price by smartphone OS, with the average iPhone going for ~$640 vs ~$280 for the average Android phone according to the latest IDC numbers. Those are unsubsidized prices of course.
For reference, $280 is roughly the price of a Galaxy Ace: 480x320 TFT screen, ARM 11 CPU, 158 MB internal storage, 278 MB RAM, HSDPA, Android 2.3 Gingerbread...
Simply put, Samsung is only winning the market share race in areas where cheap low-end phones are popular.