The 41-year-old singer said Lopilato, 29, was convinced that he wanted to hit on her male friend rather than her, reported Female First.
Recalling their first meeting, Buble said, "She walked in this room with a man, and the man was so good looking that he made Brad Pitt look dumpy, so I assumed they were together. I naturally assumed that this was her boyfriend or her husband, so I refused to hit on her.
"I finally said, 'You guys are such a beautiful couple,' and he said, 'We're not together.' He said, 'She came because she likes you.' And at the same time, she was on the phone texting her mom saying, 'Oh my God, Michael Buble is all over my friend. He's so gay."
Buble has two sons with the actress, including Noah, 3, and 10-months-old Elias.