Last week, it was reported that the General Hospital actress had been cast as a new love interest for Barney (Neil Patrick Harris).
"Barney takes note of this girl, and she catches his attention," Thomas told Entertainment Weekly. "She catches his eye a little bit, and it's interesting to watch Barney wrestle with 'Do I jump in, go 100 percent, full-throttle... or do I talk to this girl who's kind of intriguing?'"
He continued: "The whole thing catches Barney by surprise, and it's always fun to watch Barney Stinson get caught by surprise."
Despite the introduction of Boniadi's character Sarah, Thomas also refused to rule out a future reunion between Barney and Robin (Cobie Smulders).
"We don't like to close doors on this show too much and certainly Barney and Robin is always a fascinating topic for us," he insisted. "I will say is that we would never rule out the possibility of rekindling Barney and Robin somewhere down the road."
How I Met Your Mother airs on Mondays at 8/7c on CBS.