There are theories of what the small boats can do to warships. This probably stems from the terrorist attack on the USS Cole & Iran's threats to use such strategies in the Gulf of Hormuz. I am sure the USN would have by now thought of & be prepared with counter-measures. One must remember that experience in actual sea battles is vital and important, and the USN has that experience from way back, including WW II (Coral Sea, Midway etc. etc). China has the experience in land battles i.e. guerilla warfare etc. However, with all its show of many new warships, submarines etc., the PLA-N has "zero" major sea encounters/battles. It's the well trained & experienced Officers, Men & Women, not only the "flashy ships" that make a REAL Navy. I think the Chinese Admiral's comment is just part of psychological warfare. Not wise to "try" the USN or underestimate the capabilities of a few other Navies of the Asia Pacific countries especially Japan.
I think the admiral was only making reference to the zumwalt ship itself rather than entire navies... and I don't think anyone should be taking his words too seriously anyway, given his previous statements about the invasion of iraq etc.
BUT I will say that there is some merit to the use of swarm tactics against large surface combatants -- if they're alone, in littoral, shore waters. But the thing is zumwalts and other destroyers, cruisers or carriers will be operating in groups, likely not in the littorals.. so even if small boats have small profiles and say are not detected until they are a few dozen kms out, a good portion of them can be destroyed before they are able to get within bombing distance (unless they are armed with small AshMs). most ships are armed with high cal machine guns which are probably more suited to dealing with swarms of small boats than the likes of ciws, because there are only a couple of ciws mounts on most ships and cannot sustain fire for very long.
And I agree with montyp, the lack of experience does not mean they cannot become a potent force with good training and organization.
I wonder what the correlation between the ability of being able to indigenously build flashy ships and naval professionalism/potency is.