Amano is just a guy that was pretty good at making aquariums, but really good at making money.
One guy cannot decide plants acceptable in a 'nature' scape. (any live plant is a nature scape?)
I think it more refers to a wild and natural look, as opposed to Dutch or iwagumi.
If you think it will look good, hit it. That fact that he contradicts himself is enough to show it does not matter.