See my other comment here on implicit patent grants: https://news.ycombinator.com/item?id=15051166

I doubt some statement of opinion in some out-of-the-way place that did not accompany the software directly would hold up in court.

That said, your point on uncertainty is why many people prefer the Apache2 License or the GPL3 which have an explicit patent grant (but not a one-sided grant like in Facebook's PATENTS file).