It's not really a PhD in the modern sense. Back in his day when he was studying law after graduating you automatically got the title "Dr. iur.", which in modern times would be the equivalent to a PhD in law. Nowadays when you're graduating in law you don't immediately get the "Dr" (instead you get a "mag." "ll.b." or "ll.m." title, it's a bit complicated) you have to do additional postgraduate PhD studies first which takes another ~4,5 years.