Weird the dad would tell you he asked his kid that. I would expect any diligent parent to ask questions, but not why they would tell you they ask their child.
The response that comes to mind for when a parent tells you they asked their child if you got mad would be something along the lines of "everybody gets mad at times...what is important is HOW they get mad, not IF hey get mad". If you find them making such comments frequently then you'll need to right out ask them "it seems like you ask this frequently, are you having concerns about how I interact with your child" and get down to the root cause now so they are not going on info a young child passes on!!