I wouldn't trust that counter. You should be burning more than 168 extra calories in 40 mins, unless you're soft pedaling and aren't even close to breaking a sweat. But for a guy of your size, even soft pedaling should burn at least 400 calories an hour, so 266 or so for 40 minutes.
I use a heart rate monitor connected to a bunch of fitness/cycling apps that are set up for my weight and life habits - I typically burn anywhere from 500 to 1000 calories an hour on the bike. And those are "active calories", i.e. calories on top of my BMR (basal metabolic rate).