It looks like that's because its using GitHub's timeline API, which -- in addition to GitHub's general repository API -- only retrieves repositories which are actually rooted at the given user. Sort of a shame; I feel like most people's most interesting/important open source activity is on repositories which they don't own.
At the same time, this probably cuts down on "me too" contributions. I have a repo that has been gaining popularity lately and have been flooded with pull requests that do nothing but add a jshint file or other dev environment changes.
It looks like that's because its using GitHub's timeline API, which -- in addition to GitHub's general repository API -- only retrieves repositories which are actually rooted at the given user. Sort of a shame; I feel like most people's most interesting/important open source activity is on repositories which they don't own.