Sounds like he could be nightshade intolerant. Also, he may have histamine intolerance. Tomatoes, balsamic, black pepper and avocado are all strongly high histamine / histamine promoting, which can cause very rapid abdominal bloating.
I am both nightshade and histamine intolerant. I can tolerate peppers and potatoes in moderation, but am very intolerant of tomatoes and aubergines.
I suggest trying the same breakfast with raw tomatoes to see if that bloats him. I've found the same as primalsun - raw vegetables are much more potent in inducing a reaction when it occurs.
F 5 ft 3. HW: 196 lbs. Primal SW (May 2011): 182 lbs (42% BF)... W June '12: 160 lbs (29% BF) (UK size 12, US size 8). GW: ~24% BF - have ditched the scales til I fit into a pair of UK size 10 bootcut jeans. Currently aligning towards 'The Perfect Health Diet' having swapped some fat for potatoes.