We ask for the commit we want and connect to a node with BitTorrent, but once connected we conduct this Smart Protocol negotiation in an overlay connection on top of the BitTorrent wire protocol, in what’s called a BitTorrent Extension. Then the remote node makes us a packfile and tells us the hash of that packfile, and then we start downloading that packfile from it and any other nodes who are seeding it using Standard BitTorrent.
The disadvantage here is that any given file in the repo could be stored in an ever increasing number of packfiles. Each existing version of the repo will generate a new packfile to get it to the newest version, and it's up to the authenticated masters to generate and seed each of those packfiles, while peers either do or do not cache these replicated datas. In short, this means of syndicating updates ignores the Merkle-DAG-ness (DAG-osity?) of Git.
The un-updateability of torrents is something that seems to seriously limit it's use. There are a lot of interesting attempts to hack around this- LiveStreaming and Nightweb are two that spring to mind. https://www.tribler.org/StreamingExperiment/ https://sekao.net/nightweb/protocol.html