How was it established that the tablet used in the study is not digestible?
I do not know how the actual study was performed because the news release does not tell us. I am just guessing that they comparied a solid tablet with a liquid mix of grape powder - the liquid will absorb quicker and better compared to the tablet which needs enzymes to break it down. So the tablet may metaphorically move through your digestive tract without being absorbed; or more accurately put, without being absorbed much. If that is what they did in this study then it is not an apples to apples comparison; or shall we say liquid to liquid study.