I guess you've read that the same person had a gallstone that was surgically removed later. That makes it very likely that the ones flushed out were real.
No, actually just the opposite. The "stones" she supposedly passed were 2.5cm, larger than can physically pass through the bile ducts. Then they refer to the single stone as "large", which implies it was larger than the 2.5cm most likely olive oil blobs she passed. Considering how slow gallstones take to grow this would mean that the real gallstone never came out in the first place since the flushes do not work.