Hi,
First, pushing is altering development to increase contrast. How you rate your film does not determine whether or not you are pushing. This only determines how you are exposing. Pushing refers to a development technique, not to a film rating. You cannot technically push without, er....pushing!
So, what Kodak is saying is simply that the film can easily survive one stop of underexposure without being pushed.
FWIW, most black and white films can do this as well. T-Max simply handles it a little better due to its inherently near-linear response to light. For my personal shooting, I think of T-Max as having a lot of the same uses as digital: Low contrast and/or low light scenes, where underexposure (often extreme underexposure) is unavoidable. This is where digital and T-Max really work best for what I shoot. (Of course, T-Max is more flexible and has more latitude, as does negative film in general, IMO.)
Your roll should be fine. I would not push it. It is more likely that you will make the shots at 400 harder to print by pushing than it would be to print the underexposed shots at 800, even with normal development. This is because it is generally easier and more "natural" looking to add contrast to a print using simple printing methods (such as contrast filters) than it is to lower contrast with the same methods.
