There are no changes in the APi, I confirm.
Look at the link below, use it with your
YOUR_WEB_API_KEY and
YOUR_STEAM_ID_64 and try it, you will see the
gameextrainfo required is not present (I tried with your SteamID64 right now)
https://api.steampowered.com/ISteamUser/GetPlayerSummaries/v0002/?key=YOUR_WEB_API_KEY&steamids=YOUR_STEAM_ID_64
The API (as part of the private data) should give both GAMEID and GAMEEXTRAINFO, in your case the latter is missing and the logic displays the natural fallback I coded, aka "game unknown".
from the Steam¡s API documentation wrote:
Private Data
.....
gameid
If the user is currently in-game, this value will be returned and set to the gameid of that game.
gameextrainfo
If the user is currently in-game, this will be the name of the game they are playing. This may be the name of a non-Steam game shortcut.
.....
You are currently IN GAME since your GAMEID is:
"gameid": "10"
..
time to ask those guys about that maybe?
Also I have found this discussion, dunno if effectively relates since I stopped reading it after a dozen of replies
https://www.reddit.com/r/Steam/comments/6li55u/changes_in_steam_api_a_dozen_removed_games_no/