Errm... not sure where you read that. Burning calories is a VERY complex calculation, as it differs between everyone. You have a source on that statistic?
Warning: Long answer below. Summary: swimming definitely too hard, hiking maybe too hard, and cycling might be ok to try to quantify in such a way. If interested in detail, read it all

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Consider a 400 pound man running/walking a mile vs. a 140 pound long distance runner. The 400 pound man simply must expend more calories to move more mass- it's simple physics- otherwise you'd have a crazy world where a car that weighs 4000 pounds gets the same mileage as a lighter one. It would violate conservation of energy, if I remember my physics correctly (probably not).
Age and physical condition also plays a part. Someone who knows how to run is more efficient. I used to be on a swim team. I ended up using less effort and going faster when I was a good swimmer. Also factor in muscles and resting metabolic rates- when you're young/full of muscle, you burn more calories.
Swimming is a very different kettle of fish. For most people, swimming a mile will be quite a tiring activity, so you will be incredibly less efficient after a little time- if you think running a mile is bad, do a mile swim. So, if they get tired and aren't really swimming at a sprint, does it still count?Record swim for a mile in just under 15 minutes (there's a reason the olympics doesn't really feature it). Compare that to a mile, where it is closer to 3 minutes. So, a very different amount of stamina. In addition, I can tell you, water temperature makes a HUGE difference. I like it pretty cold, as I do sprints (longest I would do was 200 yard); but I can imagine if you were swimming for a much longer time warmer might be better.
Road cycling might be a good comparison, as it is a fast paced/non-fatiguing (relatively) activity. Hiking is different again, with uphill, downhill, and losing your footing being important factors in how fast you'll be comfortable moving at.
I've seen some articles that said swimming burns up to 800 calories an hour. Not sure if that's true; what I can speak to is that when I was on training trips for 2 weeks, I'd easily eat 6-8000 calories a day, and would sometimes even lose weight. We did 2 2 hour sessions; 10,000 yards generally, with sometimes some low-impact activity in the afternoon. I'd usually eat maybe 3500 a day normally, and we did 1 1/2 hour practices 5 days a week.
Sorry for the long answer, but it's rather complex.
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