Help with understanding strange capacitor configuration arrangement
Indeed it's a pretty horrible layout, though almost anything is acceptable with a 7805 and a digital circuit.

The ceramic disk capacitors (last-century single layer version of today's ubiquitous MLCC chip capacitors) have lower impedance at high frequencies than the aluminum electrolytics (which have a certain amount of inductance and ESR), however they are limited in value so they can't cover the whole frequency range. So you get a lower overall impedance (and some damping) at a lower overall cost by combining two different types and values of capacitors (a 100uF ceramic disk capacitor would probably be the size of a dinner plate). 

The ground trace layout is the most egregious- there should be a star connection at the input filter capacitors. 100uF on the output is unnecessarily large, but it won't hurt anything (a 100uF/10V cap is pretty small physically). 100uF on the input may or may not be sufficient.