Not sure how you explained it. How detailed do you think you need? Do you know any engineers/physics types that could draw him a force diagram? Did you try explaining that it depended on the strength of the table materials (at some point the table wouldn't hold the lion? An example at home might be a cheap overloaded bookshelf with the shelves bowing in the middle (we had lots of those when I was growing up).
Science4kids has a Level 1 Physics book that might have some information on forces/strength. I couldn't tell from the sample.
