The thread title is extremely misleading. While I think that, in general this may be somewhat true I would like to point out a few things:
First: This is probably only truthful in terms of economic left and right and has nothing to do with political or social ideas of liberal and conservative. Certainly correlations could and probably do exist between the two, but that doesn't really mean much and shouldn't be used as a means to automatically right off the economic thoughts of self described liberals. I could still have a moderate to traditionally conservative economic stance and still overall (when my political, international and social stances are taken into account) be much more liberal than you and still be much better educated in economics. Hopefully that goes without saying though.
second: This does not mean that anything economic that is traditionally supported by liberals is a bad economic policy or is one that is devoid of strong and educated economic backing. Examples would include government intervention into insurance markets, certain credit markets, regulations concerning negative externalities such as pollution, government production of certain pure public goods and so on. This does not mean that supply side economic efforts are always a better idea than Keynesian economic practices and it certainly doesn't mean that crap like Rothbardian economic theory is superior to economic ideologies that advocate a mixed economic system.
third: The statement is, in and of itself not completely true, because once you go so far towards pure capitalism, or in certain other areas of traditionally conservative economic thought, there is definitely a drop off point in terms of understanding economics and support. In fact I would say that anarcho-capitalists are probably just as ignorant of rudimentary economics as perhaps say a socialist or even a communist. I wouldn't suggest that the scale is a perfect bell curve though.
fourth: Obviously, like anything else that makes such claims this is not true for everyone who holds liberal and conservative economic viewpoints. Something which also hopefully goes without saying.