In that quote, there is a kernel of truth, with a candy-coating of editorializing.
If you look at the February 2018 USPTO statistics for the PTAB as an example, the final page shows some stats.
Final written decisions:
Instituted claims unpatentable
No claims: 389 (19%)
Some claims: 323 (16%)
All claims: 1304 (65%)
So one way to view it is 81% of patents do not hold up when challenged (in that at least one claim is found unpatentable). I think 81% would be regarded as a significant percentage.
Of course, we don't know if the quotee meant PTAB, or court, or what. But this at least indicates that the underlying statistics referred to by the quote, on their face, are plausible.
The quote itself is very misleading, since it implies that this can be extrapolated across all patents ("in circulation", whatever that means). While this sounds good, it is almost certainly not the case.
First, there is no way to know what would happen to all cases generally, and anyone professing to know is only speculating.
A patent will generally only be challenged if the challenger has a reasonable expectation of winning. Why throw money away otherwise? So immediately you will see that only weak patents will be in a position to have a decision issued. The non-challenged cases are inherently not analogous.
In fact, it could well be that 99% of issued patents would pass through the IPR process unscathed (if this ever occurred), and all the current invalidations relate only to the other 1%. This would be consistent with the statistics too. But you can't get attention by saying "most patents are pretty good, no cause for alarm".