The site you are talking about is quite right. If you spend all your practice time on what they say at the end of it you'll be able to play those songs and can have a stab at others.
If however you spent a quarter of the time learning about chord tones and then get the chords to a song you'd be playing your own parts or copping the parts already played and sound good doing it.
Both ways will get you somewhere, where do you want to be?