I was playing a game with someone and they said they do because planeswalkers can't attack, so the tokens created by them count as commander creatures. Is that true? I can't find any rules that talk about this.
Rule 903.3 says
Each deck has a legendary creature card designated as its commander. This designation is not a characteristic of the object represented by the card; rather, it is an attribute of the card itself. The card retains this designation even when it changes zones.
Only the cards that start the game as commanders count as commanders and can deal commander damage.