FYI, many modern sailing yachts are predominantly made of fiber glass, which is also not nearly as radar reflective as metal. But "not as radar reflective as metal" and "not radar reflective" are two very different things. So the hull and primary structure most certainly reflected radar.
Now consider that there's still a LOT of metal bits and pieces on both wooden and fiberglass hulled vessels. If memory serves, HMS Victory was equipped with 104 iron guns at Trafalgar, and tons and tons of iron cannon balls. Plus there are all sorts of metal fittings, cleats, bollards, rings, eyebolts, barrel bands, mast bands, chains, brass/copper lanterns, copper cooking tools, etc etc all over the ship, each a separate radar reflector. In other words, LOTS of metal to reflect radar.