As someone who has never published code in a public repository or even written a blog despite many years promising myself to publish this or that project on github, and knowing a good number of excellent developers in a similar situation, I know very much not to give undue importance to these. Like @oded says, there is no better way to make an assessment than to engage a prospect in a problem solving exercise. Some people can talk (or write) impressively about things that they know little about in practice - that is their gift. Equally, some really good practitioners can find it difficult to express themselves - that is the way they are.
I would usually ask for code samples which may or may not be in a public repository, but these can only give you part of the picture. For me software development is more about a certain type of mindset - more so than knowing this or that language or writing code in this or that style or applying this or that methodology.
Just in passing, I know two people, one a company director and the other a lecturer who I think are great programmers that are not software developers !