"You're following me!" Perry, 32, joked on camera during an Instagram story that included the label, "stage 5 clinger."
"I am -- everywhere," Horan replied, while making a silly face.
Last week, the pop singer implied that the One Direction crooner might have a Graduate-style crush on her.
"I see [Niall] around all the time," she told the Australian morning radio show Fitzy & Wippa on Nova 96.9 FM. "He's always trying to like, get my number, to like, maybe flirt with me but I'm like, 'I could babysit you. I'm like your mom!'"
All joking aside, Perry admitted that the label-mates do share a special bond.
"Niall's amazing, I love him, and I think we feel very connected in a way because I, like, helped him get through The X Factor to join his group," she said on Wednesday. "He's become a big star and I'm like, 'Cool, I guess that means I have taste?' I don't know what that means."
When Horan, 23, heard about Perry's flirting accusations, he chalked up any noticeable affection for the pop singer to strictly friendship.
"Katy, please stop being mean to me," the singer joked on Australia's The Project. "She's just finding any excuse now to just patronize me and go around spreading rumors about me. I just want to be your friend!"
As for the comment about Perry being old enough to be his mother? "I mean, she is talking like she is about 55 years older than me. She is not that much older than me," Horan said of the pair's nine-year age difference.
Perry continued the shenanigans the following day on the same show, stating, "[Niall] wants to go out on a date. Have you ever seen the movie, The Graduate? That's kinda what it feels like. I could be his mom!"