Pogba won the decisive second-half penalty which Bruno Fernandes converted, as United secured a 2-1 win over Aston Villa in a thrilling clash at Old Trafford.
Anthony Martial fired United ahead on 40 minutes before Bertrand Traore levelled matters, only for referee Michael Oliver to point to the spot following Douglas Luiz's challenge on Pogba before the hour mark.
But Smith reckoned Pogba had tripped himself up and he said: "He trips himself over. If there's that much doubt then VAR should send the referee over to look at it himself. I'm dumbfounded that didn't happen.
"My view was that it was a penalty from where I was stood.
“I thought Douglas Luiz got too tight with Paul Pogba, but then I've just gone in and seen it back and I think he's just tripped himself up.
“I think there's enough doubt there to send the referee over to the screen."
United have now gone 10 games unbeaten in the league to move alongside leaders Liverpool, with just goal difference separating the bitter rivals.
Ole Gunnar Solskjaer is refusing to consider a title tussle between the two clubs, but admits United are getting stronger by the week.
He said: "We are very happy with the position we are in. It's such a big difference from 12 months ago. It's a good position but we need to improve and keep getting better.
"Of course we are happy with what we are doing. We have shown we have improved a lot in a year.
“We have improved immensely. We are getting fitter and fitter and stronger and stronger.
"I think the league and the season is going to be so tight.
“We've just got to keep working and improving as a team, but every time you win a game you take one step further. You've just got to accumulate the points. They all count the same."