Also from [3]:
> Invading propagules begin as residents in a potential donor region (stage 0), some of which are taken into the transport vector (stage I), usually by humans. If these propagules survive transport and release to become introduced (stage II), they have the potential to establish (stage III) in a novel environment.
Note that 'stage I' notes 'usually by humans', not 'by humans'. Ie. a species which uses some natural phenomena as a transport vector can still be considered an invasive species. [1] says similar - "Human actions are the primary means of invasive species introductions." - implying that non-human methods are also possible for invasive species introductions.
It's nonsensical to say that as soon as something migrates using a natural phenomena that it becomes a 'native' to that area.
[1] https://www.invasivespeciesinfo.gov/whatis.shtml [2] https://www.invasivespeciesinfo.gov/toolkit/vectors.shtml [3] http://www.esf.edu/efb/parry/502_reading/colautti2004.pdf
>if Kudzu somehow (perhaps a form of geological change happens in thousands of years like a land bridge, or continental shift, or maybe the seeds are simply moved by some migrating population of bird) reached these new ecosystems by it's own means, it would still be an invasive species.
If the plant migrated on it's own than that area is now its native area.