The key is "believe it was real". Had they said "know it was real", that would be different.
Do you understand how reporting and journalism works? Rather - do you understand how
english works?
You can't "know" something unless you have a first-hand account of it, or there are enough first-hand sources to corroborate something. You "believe" something when it fits everything you "know" to be real, and there is no reason to feel something is fake. So if you know what Rob Ford looks like and sounds like, and you see a video that clearly shows that man you "know" in it, you believe it to be real. Without having been there, you can't "know" it to be real. The second the reporters say "We know the video is real", they will be held to account for how they know it - IE, how do they
know - were you there? Did they see it being taken? No? Then how do you
know it's real? Not to mention, if it does turn out to be an
incredibly good fake, you can get into quite a lot of legal trouble for saying something was real when it wasn't.
All of that being said, that isn't reason to believe it IS fake - It's just to explain why they make a linguistic distinction between believe/know. We rely on second-hand information all the time, and we rely on journalists constantly to tell us things accurately so that we can come to "know" the things that otherwise we couldn't - and this is no different. Whether or not you
trust said journalists is up to you, and that's generally what the issue/question is when people talk about the video. The entirety of the Fords' rebuttal to the video is "Don't trust the source! Don't trust the source! Look over here, don't pay attention to them!"