That is correct. A study does not have to involve drugs that are available for prescription. Actually, they often are not. This is where manufacturers get their data to present to the FDA.
However, Rebebcca, could you please provide a link to this study you are talking about? I looked at all the studies listed inder the tab "studies" on the SIBO website you mentioned http://www.siboinfo.com/dr-siebeckers-bio.html, but I could not find it. I did not see it mentioned in the blog either.
But generally, the way that generics get approved is that they have to prove that they are essentially the same in regard to the intended treatment effect, as the brand name. Sometimes there are individual indiosyncracies or intolerances that make one form better than another. But, it is not a blanket rule.