Fairly sure this is not true, unless you have a source. Drew did all the client side work in python/librsync to get going.
Ok, may have been inspired by. Here's some relevant backstory from 2011:
https://www.wired.com/2011/12/backdrop-dropbox/
Caveats: https://www.cis.upenn.edu/~bcpierce/unison/download/releases...
Symbolic links: https://www.cis.upenn.edu/~bcpierce/unison/download/releases...
Permissions: https://www.cis.upenn.edu/~bcpierce/unison/download/releases...
Cross platform issues (unsupported characters across operating systems and file systems): https://www.cis.upenn.edu/~bcpierce/unison/download/releases...
Edit: Inspired by the the Unison Spec (published on 2004) which may be why we have conflict files etc. when using Dropbox http://www.cis.upenn.edu/~bcpierce/papers/unisonspec.pdf