No, not dumb -- or, at least, you can't prove it by this particular instance. I asked for exactly what the web site told me to ask for and got the wrong motor as well (I made mine fit, it took about 2 days). _Later_ I found out that GM used two different motors in that application, as Mike pointed out, and I'm guessing that some retail parts stores will default to premium models unless challenged.
That guy needs to update his web page if he intends for it to be truly useful to fellow Jeepers.