I'd probably enter the amount the machine told me, although that seems really low for 30 mins on the elliptical. Do you have any incline or resistance? I find that when I have a moderate amount of both, the number on the machine tends to be pretty close to what FS would estimate for that exercise. You might also want to see what FS tells you for light intensity on an exercise machine.
And yes, running for real is significantly different.
As a general question, do we think that the value the machine reads is fairly accurate, as long as you enter age and weight? I assume it is(since the machine clearly knows exactly what you did! but I sometimes wonder.