Important difference to point out. You phrasing tripped me up though, and I want to point out that Senator Ron Wyden (D-OR) (who's linked above) is also upset about ACTA not being considered a treaty.

So members of both houses are angry (thus Congress in general), but only the Senate's approval is needed for a treaty. It is unconstitutional for a president to enter into a treaty w/o Senate approval.

Article II, Section 2, Paragraph II of the Constitution states that the President: "shall have Power, by and with the Advice and Consent of the Senate, to make Treaties, provided two thirds of the Senators present concur"

(Sorry, I've recently gotten into constitutional law and wanted to post this FYI)

Maybe he had help from Sen. Wyden. I know he was trying to open up ACTA and get it ratified by the Senate.