Although the Gunners needed to come from behind to prevail in Austria, Thomas starred on his first start for the Premier League giants since joining from Atletico Madrid.
The Ghana international made an immediate impression on Keown, who was quick to compare the player to club legend Patrick Vieira.
Speaking to BT Sport, Keown said: "I think you know when you see a player immediately add that touch of class, who wants to play and makes things happen. He's so silky smooth, he's oozed class and been everywhere.
"This is where he looks like Vieira for me when he's travelling with the ball and making things happen."
Thomas will hope to feature when Arsenal play host to Leicester City in the Premier League on Sunday evening.