They're not lying, they're just not truthful about their eating habits. Walking for an hour takes about 500 calories or so, and if you're a fat fuck with no impulse control it's very easy to stack up the caloric intake. "Gym of life" means very little if it's just casual walking and cycling. Don't get me wrong, it's good for the heart and generally healthy and everyone should walk and cycle more, but it won't get a fat fuck thin if they don't diet hard.
What annoys me about this claim of the "Gym of life" is that it doesn't match with the society they want.
- 15 Minutes Cities: If one lives in a 15 minute city, they may walk 15 minutes to and from work to where they live but how much walking is actual being done. As you said, its probably around 1 hour given the 30 minute commute and walking around an office.
- Alcohol consumption: Many if not most of the proponents of 15 minute cities use the consumption of alcohol as a benefit of public transportation. But if they have two drinks, that's about 250 calories.
- Third place slop: When not discussing their "fascination" with alcohol consumption, they talk about the 3rd places like a coffee house or cafe where they can get some light refreshments or snacks but a medium cappuccino is 140 and a snack is around 160 calories to be conservative. So we add 300 calories a visit to a 3rd place.
- Transit time: For people that live close enough to mass transit systems but work farther away around a hour they may walk 15 minutes to the transit station and a short distance to their jobs but they still roughly get a hour of walking per day. But, when they are playing their Nintendo Switch, reading, etc. they aren't working out. Worse because of their commutes take more time than a car, they not only can't work out but are more likely to go to their aforementioned 3rd place and get a slop meal.
Below is what I envision for a "Gym of Life" person:
0630: Wake Up.
0645: Go to the Bodega for a Chopped Cheese or Bagel (700 Calories /500 Calories)
0700: Arrive at job or transit station.
1200: Lunch. Sweet Greens Salad or NY pizza slice with soda (550 calories)
0730 - 1630 / 1700: Get off work.
1800: Dinner (1200 calories)
2000: Alcohol or snacks plus a beverage at a 3rd space (250 Calories)
Low estimate of daily calories consumption: 2200 calories.
Calories burned by walking for a 180lbs male for 6 miles (lower end of NYC walking total): 600
BMR of 180lbs male: 1950 Calories.
Now, this might seem like a calorie deficit (350) but that's because I being more conservative with the food and drink one consumes. they are basically one small bag of chips or two more drinks away from being calories neutral or having a small surplus.
Realistically, what matters is going to the gym or taking part in an active sport for about a hour and getting off your ass every hour if you work a desk job.
That and cooking your own food will help with weight loss or maintaining a healthy weight moreso than the gym of life.