Could this genuinely teach me how to play a guitar?
Yup totally - and/or bass.
It has everything you need to know, which whilst good for the beginner, its a bit of a pest for people with any level of previous knowledge (no option to skip the basic basics).
But yes, teaches you basically from how to put the guitar on, how to hold it, how to strum etc... right up to hammer ons, bends, vibtato, slides etc. All with video lessons.
Plus there are arcade games (about 8 I think) that each target a different skill, (sliding, fretting, scales etc), which help you get better at the disciplines.
The actual game itself is awesome as there is no difficulty level you can set (like Rockband) - every song starts off at the easiest level with a few notes slowly moving down. If you hit them right (or if you know the song and fill it the bits anyways) then it starts adding in more notes that come down the highway.
Each section of a song (and songs can be broken into 10-20 sections depending) have an XP-like bar. So the better you get at a section (or phrase), then the more notes it gives you until you are playing every note of that bit 100%. Master all sections in a song, then you get chance to "master mode" that song, which is basically playing the song without a highway on the screen.
Its such a good idea and really works. The XP is saved each time you play the song (or you can reset it) so the next time you play it, it gives you the notes at the level you have reached. It really benefits playing a song over and over a few times in a row as you really start to learn the complex bits - just like learning IRL actually.
Last night I had a go of Where Is My Mind by the Pixies (a song I knew how to play more or less using chords). Instead of playing what I (thought I) knew, I played along with the onscreen track. First goes was absolutely awful, missing loads of notes, wrong notes etc... sounded like a cat being raped.
By about the 5th or 6th go, it was sounding awesome and I'm still a fair way from mastering it.
Oh also, you cant 'fail' a song like in Rockband, so its a lot less frustrating. If you start doing bad, they dynamically scale back the difficulty whilst you are playing till you pick up again. Very good.
So yes, you could most definitely learn guitaring from playing the songs in this without doubt.
having so much fun. 
