Solution:The process list gave it away. I guess the installer detected a rpm binary and assumed that I was in a rpm based environment? I don't actually use 'rpm' on this system so I apt-get removed it. After this, the nvidia installer works fine.
On second thought this isn't a solution, but rather a workaround. If anybody figures out what might be wrong here, and knows how I might install the nvidia drivers without removing the 'rpm' package I'd appreciate it.
Thanks
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