Trundle toolkit missing information (debatable)

So a while back Phreak claimed that Trundle's ult also stole damage reduction, however this information is not on his toolkit, the official trundle page on leagueoflegends.com, or on his wiki page. Is this statement true? If so please indicate this on his toolkit. Thank you. P.S. I am posting this in "report a bug" because if this is true it should be in his toolkit, and it is not.