With the match already four minutes into added time, Charlie Reilly crossed from Dundee's right, and Wright went down with Brandon in close proximity.
Referee Ross Hardie pointed to the spot and booked the Kilmarnock defender.
VAR had to establish whether Wright was onside and took around nine minutes to do so, with Hardie going over to the monitor towards the end of that time.
McCann later indicated there were technical issues with VAR and that the officials "couldn't calibrate the machine" to draw the lines and "had to support the on-field decision".
So, penalty Dundee. But Westley could not get the better of Roos.
"It was chaos," McCann said. "It's a ridiculous situation when the referee's got to come over and he's got to judge whether that's offside or not.
"I think it was offside. I don't think it's a penalty either. It's so soft. There's a wee bit of contact but this is a contact sport, he's clearly not going to get on the ball."
Dundee manager Steven Pressley said he does not blame the officials but rather that the technology is not fit for purpose.
"The reality is that our technology in this country isn't up to speed," he said. "As a result, you get difficult situations like we did at the end of the game.
Asked how the situation could be improved, Pressley replied: "With better technology, it's as simple as that - investment in better technology."