I will back that up. I slipped in them the first time I wore them. It wasn't even a very slippery surface.
I HATE my Nasu's and slipping is one of the reasons. They are very slick soles for me.
Everyone I know LOVES their Nasu's and Marshalls. The Nasu's do not have the correct support for my feet. They have a very flexible sole. While some folks think that is awesome and comfortable, I prefer something more rigid.
I finally gave away my Kozos from Japan because they hurt my feet no matter what I did. I tried socks, two socks, no socks, with arch inserts, without inserts, with gel soles, etc. They were painful to wear no matter what. And one thing I have learned in 55 years on this Earth: Don't wear shoes that hurt. Don't do it, nothing good ever comes of it.
I love my Targhee II's and my Bryce Keens, both are waterproof. I also loved my DeLaveagas while they lasted. However, I will never buy another pair of Nasu's or Marshalls. Different strokes for different folks. Again, everyone I know LOVES their Nasu's except me.
FYI, I have very wide feet usually wear a men's 9 and choose Keens in Mens 9.5 (with Walk-Fit inserts to prevent Planar Fasciitis flare ups).