it is not a High ISO problem, your camera has noting wrong, this is cause by using a shutter speed faster the frequency of the florescent light, shoot lower than 1/50 will not be have issue at all.
fluorescent flicker makes your photo have different colour temperature within the same photo. But if you are referring to the pixelation of the light fading from the center to the left edge, I think it is due to JPG compression loss.