He might be 'fairly relaxed' about it, but what entitles you to expect 'bystanders' to excuse a toddler's 'tantrum or two' in the close confines of an airliner?
The fact that I would (have been; will be) happy to put up with it myself in situations where I'm the 'bystander'. If crying toddlers is all you have to worry about in life, you're a lucky person.
There is behaviour that parents shouldn't put up with, obviously.