It’s hyperbolic, but it makes a good point.
There’s more to it than seeing the cross-pollination or antecedents of one’s native language. It’s difficult to gain an objective perspective on the language in which you’ve been immersed all of your life, and supplies the voice for your thoughts (and to some extent shapes them). In that sense, one knows nothing of it; in much the same way, a fish knows nothing of water.
To arrive at an objective perspective requires that you step away from your native language into a different way of structuring meaning. It’s in looking back at your own language from this different one that you can now see and appreciate what makes it unique. I’m reminded of the way that astronauts say that their understanding of Earth was viscerally transformed by seeing it from the vantage point of space.
I would say, then, that it’s the differences more than the similarities among languages that make this change of perspective possible.