The only shaky information is the fact he said the second professor was Sycamore, which could be a mixup if we later find out about Patrice (which I doubt they'll announce before release) and the fact he said there would be two rivals, when there seems to be five. That could be explained by the fact his playtest version may have started slightly later in the game and he never met the rest or simply that the rest of the friends aren't really rivals, similar to how Bianca.
First off, there's no indication of there being five rivals. You have a lot of friends, but they're not all rivals. Second, I'd have to double-check, but he never did say Sycamore was "the second professor". In addition, a lot of the things he said were paraphrased by WPM. This was pointed out when he talked about how his source had specifically used the word "Sky Battle", but he never reported those words. For all we know, he could have also misheard the source on a few points, missing the fact that maybe the professor's name is Patrice Sycamore or something.
All in all, the source is apparently completely legit, and the errors mostly just come from communication issues and people making assumptions. Ah, I missed this... Back in the day, I used to have a reputation in another (non-Pokemon) community for keeping leaks/announcements sorted between the literal statements and possible interpretations. I wish I had the direct source for these rumors, so I could do the same here... --- Socran's Razor: "Never attribute to massive stupidity by someone else, what could be explained by a tiny bit of stupidity on your own part."