That just depends on how you define "distributed". If it means "running on multiple machines", then even centralized protocols are distributed, since a part of the computation is running on your computer.
In context of protocols like Mastodon, if the end-user devices aren't primary holders of data, then I don't call it distributed. It's just decentralized. I guess that way, "distributed" necessarily implies peer-to-peer.
In context of protocols like Mastodon, if the end-user devices aren't primary holders of data, then I don't call it distributed. It's just decentralized. I guess that way, "distributed" necessarily implies peer-to-peer.