Glassblowers in old unregulated factories with no modern safety standards were exposed to tremendous amounts of radiation. That exposure included infrared light but there was also ultraviolet exposure and even more ionizing radiation. The overall energy levels that the workers were exposed to were quite high. The workers also toiled in an extremely hot environment exposing their eyes to thermal injury. The total effect could be similar to staring at the sun! They were additionally exposed to a variety of toxic chemicals and particulate substances.
Telling people not to use near infrared saunas because they will get cataracts is like telling them not to use lights at night because looking at the sun will damage your eyes. It is an argument used by those that can not argue on the facts, since the facts do not support their argument. Tungsten lamp saunas emit very low levels of infrared energy compared to a glass factory.