"[Chua] proved that memristor behavior could not be duplicated by any circuit built using only the other three elements, which is why the memristor is truly fundamental."
Later in the article:
"Emulating the behavior of a single memristor, Chua showed, requires a circuit with at least 15 transistors and other passive elements."
Reconciliation?
I think when they say "fundamental elements" they mean the fundamental passive elements of analog circuit theory (mentioned above), as opposed to active elements like op-amps or transistors.
"For nearly 150 years, the known fundamental passive circuit elements were limited to the capacitor (discovered in 1745), the resistor (1827), and the inductor (1831)... He proved that memristor behavior could not be duplicated by any circuit built using only the other three elements, which is why the memristor is truly fundamental. "