I suspect if you counted the hours they were thinking about their work, the conclusion would be the exact opposite.
Granted, we are talking about "thinkers" here. We can think sitting on the toilet or taking a shower, and maybe even better than staring at a book.
Walking to get your juices flowing surrounded by clean air and a soothing environment would make any hiking trail a great office for any scientist or philosopher.
"It's not that I'm so smart, it's just that I stay with problems longer. "
― Albert Einstein
"Richard Feynman was fond of giving the following advice on how to be a genius. You have to keep a dozen of your favorite problems constantly present in your mind, although by and large they will lay in a dormant state. Every time you hear or read a new trick or a new result, test it against each of your twelve problems to see whether it helps. Every once in a while there will be a hit, and people will say, 'How did he do it? He must be a genius!"
- Gian-Carlo Rota, Indiscrete Thoughts