It's a possibility, also, assuming the TNG books are wrong. It's never mentioned as such, however, and with Voyager saying Transwarp is something the Federation don't have, I think it's unlikely.
Or transwarp is just a buzzword along the lines of next generation, 3G we use today. It could mean any propulsion technology that is comparable to a warp drive, but different in one or another, including drives that are actually faster (as seen in Voyager, TNG, etc.), drives using a different mechanism to achieve FTL without being faster, and drives that are warp drives that do something differently. It is also possible that "transwarp" drives were being renamed back to "warp" drives after each generation.