I don't think the messages from the IPFS daemon are related to the entries in the nginx log.
/multistream/1.0.0 is the response you get if you try to connect to the swarm port (4001 by default) for an IPFS node. Unless another part of your nginx config is responsible for this, I wonder if your node is responding to connection attempts from IPFS nodes that have 10001 configured as their swarm port (or are advertising it).
ipfs swarm peers | grep 10001 show? If it shows something, I bet these are responses to lip2p connection attempts from IPFS nodes saying they're listening on 10001. FWIW I'm currently connected to at least 5 peers with 10001 listed as a listening port.
edit: even if my guess is correct, I was just thinking that
ipfs swarm peers might not show peers with 10001 as their advertised port since you probably can't successfully connect to them (even if they're trying to connect to you).