Saints defender Steven Anderson lasted just 15 minutes after picking up a second booking in a controversial incident with Swanson, who appeared to go to ground easily.
Houston said: "Anderson has committed a foul early and got booked. For the second one I thought he was going off the park but the referee chose not to.
"For the sending-off, I thought he got a trip on him but I would have to see it again.
"One thing I would say, Danny Swanson nicked it round him and tried to get past him.
"Danny is not a cheat. In saying that, Anderson should not have been in that position having committed two yellow card offences."
Source: PA
Source: PA