People app on Windows 10 PC has been updated, and it now adds an extra panel–History–which details all your communication with that particular contact over email, phone, Skype calls and even messaging. This is in sync with your Windows 10 Mobile, and thats why you see it there.
The interesting part here is the integration that is yet incomplete, but points to the fact that it will eventually happen. As an example all messaging communication is listed in history, and when you try to open any of them, the messaging app on Windows 10 opens up, but oddest show the SMS yet. The same goes for Phone, but instead of connecting to phone it picks up Skype Calls.
The messaging app on Windows 10 as of now only supports messaging over Skype, but it does show messages from Windows 10 Mobile on Live Tile, and even on search but crashes when you try to open it. There is a Phone app also available on Windows 10 which initiates Skype calls, but IMO in future we should see solid integration where you can use these apps on Windows 10 PC, and send SMS through your phone directly, and also initiate a call.
The people app on Windows 10 Mobile was recently updated to reflect History, and now its here on Windows 10 PC as well.