Data upload to an IP I don’t know

Server Version#: latest Mac
Player Version#: latest full release
<If providing server logs please do NOT turn on verbose logging, only debug logging should be enabled>

I noticed a 186 MB upload to an IP I’m not familiar with. I converted my 5,000+ CDs and have them on my server.

Is this much data possibly because I hadn’t used my phone app in a while and the server was connecting to a Plex ip and uploaded my catalog so my phone would have the latest?

Plex doesn’t upload any of your media to their servers.

186 MB isn’t all that much. I you consider, it’s approximately the size of a single encoded album.
Did you by chance listen to your newly digitized music from a remote player?

I might have listened to one song. Not even a full song at that.

What client are you using?
Plexamp will cache some portion of the play queue. If you started playing a song, this will usually add the entire album to the queue.