Is this a mistake on this website about Gdim7

[star7]

Is this a mistake?

On the website they have the chords of A minor, VII in A minor is G major, but then they have Gdim7 (at the bottom with the other chord shapes) used a as a resolution back to A minor in the chart above. The thing is shouldn't Gdim7 be G#dim 7 in this case?

http://scaletrainer.com/minor-key-chord-progressions/

[JumpingJackFlash]

shouldn't Gdim7 be G#dim 7 in this case?

Yes. It should be G#dim (G#-B-D, with F if you want the 7th).

Also, someone should really tell the authors that when they talk about "extra tonic chord" in the first paragraph, they really mean "extra diatonic chord" - a typo I assume, but it could be very confusing to newbies.

Not the best site to learn from; I'd find a better one if I were you.

More info:

In the minor key, the sixth and seventh notes are variables. They can occur according to key signature, or they can be raised by one semitone (half-step).

So, both G and G# belong to the key of A minor (as do both F and F#), and therefore so too do the chords containing (or built on) those notes.

Usage depends on context. The G# creates a stronger pull to the tonic (A), and the F# avoids the augmented second interval that would otherwise result from F to G#.

From this came the several different "minor scales". We have harmonic minor (with the G#), and melodic minor (which uses F# and G# ascending, but descends according to key signature).