If I was in the room during a lesson when someone said that, I would feel the need to say something - but I have enough "standing" in my ward to do so without any real risk, so I don't believe everyone should speak up in real time. I probably would say something (in a soft, gentle voice) like:
"We believe in on-going revelation and further light and knowledge. I love that we don't have to believe everything we used to believe - that we can understand better and better as time moves on and more is revealed. Eternal progression is one of my favorite aspects of the Restored Gospel, and I appreciate people, even prophets, teaching what they were capable of understanding in their days. I love Elder Uchtdorf's statement a few years ago that the Restoration is not a one-time event but rather an on-going process - which means we can let go of the incorrect traditions of our own ancestors and receive on-ongoing revelation."