I think your friend is absolutely right. A fellow BF member reported on this subject a couple of years ago just after she finished her tour through the Americas with her family. She used 700c wheels. Here is the thread. I've hosted several people touring the Americas (a few going around the world) and every single one of them has had 26"-wheeled bikes. It will also be a suitable tire size for a 49-51 cm. size frame. After living in Mexico for the past three years, we too have switched to 26" wheels on our main bikes.

In regard to the bike in your link, I personally would pass. Converting 700c to 26" is not a good idea. Brake reach will be too long and even if you make it work with adaptors, my understanding is that brake performance will diminish considerably to the point of not being good for loaded touring. The smaller wheels will also have the effect of altering the intended geometry of the bike which could make it unstable and even dangerous. Have you looked at the Surly LHT w/ 26" wheels? A cheaper alternative is finding 26" rigid mountain bike from the 80s/90s, but remember that you may have to spend several hundred dollars upgrading it to make it work for your tour.