I get it, seems as though you may not...
If you read what the OP put:
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I dont see him mention anywhere that he wants to flog his brains out for an hour or that he's doing this for any other reason than not to gain weight and go out an smell the roses/get some fresh air. He may just like to ride.
... and the fact that he just got a cadence sensor somewhat implies that he doesn't have a couple of thousand dollars worth of hi-tech tomfoolery (aka power meter) strapped on his bike.
We don't even know how much time the guy spends on a bike, either. We don't even know that his "definition" or PE of "low intensity" rides are either. For all we know he could be spinning 52x17 around at 100rpm and whilsting Dixie...
As for the theory behind "burning" more calories when riding harder, that's fine to a point but only if you're taking into account time constraints. Taking Dave's examples:
200 watts burns ~720 Calories per hour
300 watts burns ~1080 Calories per hour
I could stuff several bottles on the bike and go ride all morning at 200 watts. 300 watts, well, that's a challenge and you aint gonna be seeing me ride a couple of hours at that level for a while. The net result is that I've expended more energy riding at 200 watts than I could at 300 and still be feeling pretty fresh for another ride the following day. Funnily enough that's pretty much what I'll be doing - long rides on the weekends and 90 minutes of staring at the garage floor several times a week on the trainer and I know for experience that's the way I lose weight the fastest.
As Ms Montana sings "You get the best of both worlds..."