... don't think it means what he thinks it means.
No, not in English:
dispositive - adjective
law US specialized
deciding a matter finally, or relating to the process of doing this:
No single factor is ordinarily dispositive.
The surveyor left off the original boundary lines, and that proved to be the dispositive fact in this appeal.
The chap is German, but in French (eg: dispositif), in Spanish (eg: dispositivo) and probably other languages with the same shared roots, it can also mean device or machinery, etc.