Every. Detail. Counts.
In addition to reasons why he may not have eaten the pizza, it also may define a particular strange eating habit that someone may recognize.
The picture also shows multiple people who interacted with him, which may lead to someone recalling key details, perhaps even details about the pizza, eating habits, declining to eat it due to pork (which may indicate religious beliefs). Perhaps the key details could be non pizza related, but could describe things we did not know about him. Conversely, it could be a statement that confirms or denies things we believe to be true (but may be skeptical) about him (the sister for instance, one person may recall him specifically talking about her or specifically talking about being an only child).
Heck, for all we know, MH or a family member of his could have been the owner of a famous pizza shop and that would help if a person recalled it.
Discussing the pizza is more than discussing the pizza. It is jogging ideas and looking at angles that may (or may not) lead to patterns of behavior and/or recollections of the persons he ate the pizza around.