Fat dudes burn significantly more than ~2k per day just being alive, or at least I did when I was younger. I lost significant weight on a 2300 calorie/day diet. So maybe the OP was 2500 for "being alive" and 500 for the workout?
Possible, and I considered that, which is why I put 500 cals for an intense hour-long workout, to imply that walking for a few hours will not even come close to 500 cals.
I could be wrong, but from my research and understanding, walking is one of the easiest things for us to do, only slightly more expensive than sitting up straight or standing.
On top of this, it doesn't "stack" well because of the low heart rate usage, meaning it logarithmically increases calorie costs (our bodies essentially amortize it), whereas lifting and carrying a heavy object for 20 seconds exponentially increases it.
In general cardio will always use more energy than lifting because you can simply do much more of it.
Cardio is continuous work while lifting is work done a few seconds at a time.
Walking in particular is still moving your body horizontally through space. That horizontal displacement is the biggest determinant of energy cost for any given body, all things being equal.
Running only burns slightly more per unit distance because there's slightly more vertical displacement as you're literally leaving the ground between steps.
Fat dude doing 5 hours of walking a day would have no more knees within a month. It's good to aim to be less overweight, mostly because of the cancer and CHD risks, but also because it wears the body out faster mechanically and takes more relative effort to do everything.
