The article used some components from Au Group Electronics BB0703 to illustrate how to identify the first pin or the pin polarity for SMD chips, capacitors, LED, and diodes etc.
C15 is an aluminum electrolytic capacitor, there is a black mark on the top of the capacitor which represents the "negative side" of the capacitor.
C5, C12 and C14 are tantalum capacitors, the black mark on the top of the capacitor package represents the anode (positive termination) of the capacitor.
D5 is diode S1G, which has a mark on the cathode (Negative termination).
D100 is 1N4148, which has a mark on the cathode (Negative termination).