He is probably interested in it from either a bodybuilding standpoint or from a hormone replacement standpoint. That is if you are taking testosterone replacement, pro hormones, tongkat ali, tribulus or even DHEA one might want to minimize the amount of testosterone that gets converted to estrogen or minimize the effects of estrogen or something along those lines.
In a magazine interview, P. Arnold said that resveratrol is an anti-aromatase, which prevents the conversion of testosterone to estrogen.
There are some studies that show resveratrol will bind to estrogen receptors, but weakly. There was one, I believe, that showed resveratrol bound to aromatase, thus preventing testosterone from doing so. In theory this would result in higher testosterone levels. None of this has been tested in humans.
Several years ago, in correspondence on usenet, I asked Mr. Arnold about this mechanism, in regard to another phytochemical. His opinion was that the body's homeostasis mechanisms would simply result in higher aromatase production, bringing testosterone levels back down to where they would have been without the supplement. He does recommend cycling 6-oxo, presumably before homeostasis adjusts to the supplement. It's good marketing.
Mr. Arnold has skirted the law in marketing non-testable steroids and near-steroids for a decade. He formulated and manufactured the designer steroid for BALCO. The courts interpreted the law such that any chemical with the steroid ring structure was an illegal steroid, and he went to jail for four months. I think he's been free for some time now.