It's just estimating the calories you burn based on assumed average body weight. Does it at least ask if you are male or female? If it knows you are female, it probably assumes you weigh around 150 lbs. I think that what the machines typically assume. If it isn't even asking if you are male or female, then who knows what it assuming for your body weight.
So, unfortunately, no you shouldn't trust the calories it says you are burning, unless you do actually weigh 150 lbs. But even if you could put in your weight, so there are so many other factors that impact how many calories you burn (the temperature, your heart rate, your body fat %, your own metabolic rate, etc.) that the machine still wouldn't be accurate. And, on top of all that, most of the machines are programmed to overestimate the calories burned--see the sticky on
Are the Calorie Counters on the Cardio Machines Accurate?
The bottom line is, any calculation of calories burned by exercise, whether it is done by the machine or by an online calculator is, at best, a very rough estimate, and, at worst, completely wrong. Don't trust any of them. Probably the closest you would come to an accurate estimate of calories burned is if you have your own heart rate monitor (the heart rate monitors on the machines rarely work properly in my experience--once the treadmill reported that my towel had a heart rate of 200 bpm :lol).
threadmill counts calories burned
