As seen in the attached photo, the interior of the boot is some kind of tightly woven cloth mesh facing material, over a padded layer sandwiched underneath the leather outer. Presumably the waterproofing quality is attributable to the leather treatment, which seems more impenetrable than the very natural-appearing leather outer of the Alico Tahoe.
According to the product specs above: Lining: Dri-Lex®
If it is the Dri-Lex then why isn't the backcountry listed as waterproof?
I believe the function of Dri-Lex is to wick perspiration away from the foot, not to serve as a waterproofing layer:
"In footwear applications, perspiration is moved away from the foot surface by heat and mass transfer and into the specific Dri-Lex® fabric in the lining, footbed or upper. The fabric then works in conjunction with other materials to re-distribute moisture."