They describe the obverse and the reverse, but only show the obverse. Typical.
Clodius Albinus is called a usurper because he lost out. Three men were vying for power--Septimius Severus, Clodius Albinus, and Pescennius Niger. Severus formed an alliance with Albinus until he defeated Niger--then he turned against Albinus and defeated him. Severus was a pretty nasty character and probably a lot of Romans would have been happier if Albinus had emerged the winner.
The next coin they find will be in 3987 AD. It will be a copper coin with a bust of the Sultan of Britain, since the Moslems overpopulated all of Europe by the year 3000 AD and exterminated practically everyone else.
Just imagine the excitement in a few millenia when an archaelogist unearths a trillion dollar platinum kenyan.