Hello Robyer!
Yep it was the classic steam, and from netlog, the event looks like this:
[19:00:44 1E1C] [STEAM_1] (000000001059CB98:1752) Data received
{
   "pollid": 0,
   "messages": [
      {
         "type": "typing",
         "timestamp": 236970703,
         "utc_timestamp": 1423245626,
         "steamid_from": "the_actual_steam_id_goes_here",
         "text": ""
      }
   ]
   ,
   "messagelast": 82,
   "timestamp": 236970703,
   "utc_timestamp": 1423245626,
   "messagebase": 81,
   "sectimeout": 6,
   "error": "OK"
}