Hey, Substack CTO here. We don't distribute Ghost's code at all and the only piece of code included is a client-side search library used by the third party theme. But that library is actually hotlinked and hosted on jsdelivr (via npm) with no modifications made to it what-so-ever. This includes the line at the top with the license link as Ghost originally built it
Thanks for the correction! All the better that the original tweet kept it classy, then. :)