All SCM stats related to 'core' are currently very misleading.
http://korma.wmflabs.org/browser/scm-repos.html and the SCM repository filter list on http://korma.wmflabs.org/browser/scm-contributors.html do not include "Pywikibot" or "MediaWiki". There are three projects called 'core' and they all point to:
http://korma.wmflabs.org/browser/scm-contributors.html?repository=core
Given that page list Fabian Neundorf and I (two pywikibot only developers) and Aaron Schulz and Brion Vibber (not pywikibot developers), I assume core contains pywikibot-core and mediawiki-core and something-else-core.
compat does appear to be the deprecated pywikibot-compat repo : http://korma.wmflabs.org/browser/scm-contributors.html?repository=compat