One option is you went into Internet Preferences and selected Routes and added random information knowingly and selected save, this is unlikely because you would have remembered this!
The other option is you accidently configured it during the initial internet setup phase whether done through the welcome screen interface or selected by yourself afterwards through the Internet directory and selecting "New Connection"
The other outside option is you suffer from a random corruption of the file because you reset your Amiga when the FFS was reading or writing to the Harddisk surface, of course, probably unlikely
Add solved to the title when you get a chance (you can modify your title in the initial post)
Hmmmm, just pondering what you said; perhaps the internet wizard detected certain things specific to the MB port that requires additional information (who knows what lurks in the code for whatever reason) to be written to the routes file (this could be surplus code for testing etc) and therefore corrupting it. Once you connected the ethernet cable to the PCI card and configured it the Internet still works because it just ignores the incorrect information contained in tne routes file.