That is very discouraging news, especially as Tai Chi has long had an image of helping so many people, and of being welcoming to the disabled.
In a very early class with my first instructor, a person with a serious leg injury stated, " I can't do that move... sorry, but with this knee I just can't move that way." The instructor went over and asked," Well, what can you do?" The person proceeded to move to their ability. " Do that.", the sifu said, and went on with the class.
I have had 2 instructors since, and each subscribed to that practice. I had seen disabled people, one a 4th dan, shown the door in Japanese arts due to "system issues"..... but never before in Tai Chi.
Now, can Tai Chi cause disability? I believe it can. Our first instructor taught that we should never do one of the transitional postures in he Cheng Man Ching form as it had the potential to blow out the knee. He suggested another way. (I later began to do the form with amendments based on the theories and suggestions of one of his students, Dr Chi Chiang-tao, which restores some postures and eliminates this transition). I have also been taught that exagerrated leaning, with the knee over and out beyond the foot has damage potential. Finally, there is always risk associated when one practices this as a martial art... same injury potential as any other self defense class.
Just my personal opinion, but this is a discouraging situation.