3.25Circle of Fifths now gains another layer

Earlier you learned the outside major-key sequence:

C G D A E B...

Each major has a relative minor:

C / Am

G / Em

D / Bm

A / F♯m

E / C♯m

This is exactly why Circle-of-Fifths diagrams often place the minor keys on an inner circle.

So the original chart you showed is starting to become less mysterious:

red major chord beside blue minor chord often reflects this relative-major/minor relationship.