Grealish was outstanding on the night for Villa.
Smith said, "He's a constant threat and he moves around the pitch really well into positions where people don't want to come and tackle him.
"The opposition get frustrated and two free-kicks against him end up with two goals for us.
"Knowing Jack, he'll be disappointed he hasn't got on the scoresheet himself."
The manager added: "I said at the start of the season that Villa Park is going to be big for us in terms of how we do.
"I was only looking at the table yesterday and everyone outside of the top four and Burnley has won four games maximum.
"That shows how competitive this league is. If you win three games, you'll be in the top ten and if you lose three, you'll be in the bottom five. That's just how the league seems to be this season."