The TE Q1 is built down to a very low cost, with the optical path being entirely uncompensated, and the optical configuration being super simple, as well as the sensor being physically rather small compared to the E75.
The E75 is a very, very high end camera(that I believe actually has a 640x480 detector, crippled by firmware) with much bigger, brighter(faster) lenses and layers of calibration and filtering that provides cleaner, more accurate images.
When the Q1 states that its NETD is 50mK, you can safely expect a 40-60mK variation, and it would never dip below that unless heavily temperature stabilized and cooled(which it does not allow without serious hacking).
The E75 on the other hand, is actually lying about the noise of the sensor, but not in the way that you expect - it's adding noise on top of the raw image to cripple its performance on lower end models. On a clean image from an E75, without the noise added, you can safely assume you'll be seeing no more than 30-40mK of noise, and I've personally measured it to go as low as ~28mK on my T440bx(with a true 320x240 sensor and good optics, so comparable).