This is pure speculation, but when Derick said that, I always pictured Izzy crying "daddy, I love you" before Derick spanked him. I've seen toddlers and preschool kids do that and the parents claim the child is being manipulative to avoid being hit.
On an earlier episode, when Izzy was around a year old, Derick stated in a talking head that Izzy still had some spirit left. I felt chilled wondering if Derick felt the need to "discipline" the high spirit out of poor Izzy.
Also, Jana mentioned that Izzy was a highly spirited child. He was about two.