Based on that log Armory is also spawning bitcoind - Assuming you still want to manually run bitcoind on another user you can stop Armory starting bitcoind in the GUI.
File > Settings > Uncheck "Let Armory run Bitcoin Core/bitcoind in the background"

I don't think Armory supports RPC auth via rpcuser and rpcpassword, and having those flags in the bitcoin.conf would probably cause issues connecting? Instead Armory needs to be able to read the .cookie file in the bitcoin data directory (Bitcoind/core creates this).