Does this make sense?

I burn 300 calories, about 30 mins, almost everyday using my treadmill and I'm usually exhausted and completely drenched in sweat when I'm done. I just got a new stationary bike and it is SO much easier for me to burn calories with, I can burn 500 calories in about 40 mins and barely sweat. This just doesn't make sense to me. Is this possible or is the bike's calorie meter inaccurate?