Problem: Chords Lesson Key Of C (david'o)

Hey there, I tried posting a comment under the lesson, but that hasn't worked so far, so I'll try here.

In the lesson http://www2.guitarmasterclass.net/rhythm-g...sson1/index.htm

I posted this (too lazy to rewrite ):
"there's something I don't get about this lesson. At the chords F, G and Bm7b5 the theory scale shows a 4th fret being played, yet you seem play the third.. huh?

Any help would be appreciated, cheers!"

I asked my best mate who's quite a good guitarist about it, and he said it was definitely the third which should be played (plus playing the 4th just sounds wrong). One could just say "if you know how to play it, why ask?", but I'm afraid I might get the tabbing wrong on other lessons... or that other people who don't know better learn it wrong.

I'm just utterly perplexed

Regards,
Tilman

P.S.: Apart from that, thanks a lot David'O for the lesson.. don't want this post to sound too negative, isn't my intention =)