Roman had been following his younger self's car in a taxi and discovered he was going grocery shopping, presumably before heading home. His life truly was so boring back then. Weeks of following him and all he ever did was go home or go out to eat with Harry.
Rather than following his younger self inside the store, he ended up giving the cabbie a tip to keep the car running and waited for him to come out. He wasn't expecting to see Penny come out of the store first.
What was she even doing on this side of town? She lived more than twenty minutes away from here!
He was stunned seeing her because it was the first time since that horrible morning in the ICU when she didn't look anything like herself. Her face was flushed as if she was embarrassed but she was as lively as ever when she practically sprinted to her car.