The basic building block interval of chords is the THIRD. A major third is four half steps (i.e. C to E). A minor third is three half steps (i.e. C to Eb).
If you start with a major third (C-E) then stack a minor third on that (E-G) you get a major triad (three note chord).
If you start with a minor third (C-Eb) then stack a major third on that (Eb-G) you get a minor triad.
Two major thirds give you an Augmented Triad (C-E-G#).
Two minor thirds give you a Diminished Triad (C-Eb-Gb).
If you stack on another third on top of the triad, you get a 7 chord - the variety of which depends on the combination of major and minor thirds (CMaj7, C7, Cmin7, Cmin7b5 [also known as half diminished], and Cdim7.
A diminished 7 chord consists of three minor thirds stacked one atop the other (C-Eb-Gb-A). Because there are only 12 tones in the chromatic scale - and 12 is divisible by three - if we were to stack another minor third, we arrive back at the root (one octave higher) - C-Eb-Gb-A-C... and so on. This unique bit of math means that the same four notes are used for (in this case) Cdim7, Ebdim7, Gbdim7, and Adim7... So, no, Uncle Rod did not steer you wrong.... and yes, it is easier to just use the repeating dim7 chord shape than worry about playing a plain old diminished triad.