Can Google Chrome auto updating extensions be stopped?
Yeah, it can be blocked.  There is an extension to block auto-update by extensions.  See https://chrome.google.com/webstore/detail/extension-update-disabler/pfijgddffdeabjfpkfikmkfdpaleebek

Disclaimer: I wrote it.  At this instant, I am its only user, so exercise caution.  

It provides an enable button and a disable button, which enable/disable all extensions from auto-updating.  It works by updating the manifest files to prevent/enable the extensions from finding their auto-update site.