I think the best answer to your question is that because ultimately it's the same triad chord E maj (E, G# and B). The same note (G#) he ignored on the 11 fret is still there an octave higher on the 2nd string fret9. But, although he's playing the same chord, it's a different voicing of it. The guy looks like playing 2nd, 3rd and 4th strings on fret 9 which is the first inversion 5th (B) - 3rd (G#) - root (E). The tab adds the 3rd in the bass. You can get away with playing either voicings because they sound pretty similar, but if you want to be faithful to the song, pay attention to the bass note, that will help you figure out which one is it.
Take it from a guy who used tabs for years, never "strictly" follow tabs, they're made by normal people with normal ears who often make mistakes. Use your own ears as much as you can until you no longer need tabs. Keep rocking \m/