The 39-year-old ex-pro was given his marching orders for arguing that his side should have been awarded a penalty, even though they were already 4-1 down.
However, Kewell had no complaints about the result of the match, which did not flatter Exeter.
"We went in at 2-1 and it was game on," Kewell said. "I was confident we were going to get something out of the game. But another set-piece and a mistake and we are 3-1 down.
"That is when the anger kicked in.
He continued: "I questioned the handball and you have to change a few other things because we are chasing the game. The eagle-eyed referee sees another handball, gives it to them and they miss it so we are still in it.
"Then there was a cross in the box and it was one of those 'does it hit his hand, or does it not?'. The referee says no, we are complaining, they go up the other end and score a goal.
"That was disappointing and that is when I get my marching orders. I said 'well done' to the referee; I said you can see one in the far corner but not one straight in front of you."
The 'Magpies' will have the chance to get their first win of the season when they play Stevenage at home on Saturday, September 15.