Well, first of all, it's two quarks and two anti-quarks. Second, you'll note that that's the same as two mesons glued together (each with one quark and one anti-quark). And as the original article states, there is controversy about whether in fact this is a new type of particle... or just two mesons.
"One side proposes that the particle is actually a union of two ordinary particles called mesons .... Other theorists have tentatively labelled the new particle a true tetraquark — four quarks stuck together tightly to form a compact ball. Within the ball, two quarks are bound together, as are two antiquarks."
As for the actual number of different quarks, there are actually six (up down strange charm top bottom). Or 18 if you count them by color variant (red-up, blue-up, green-up, etc.).