TSA security looks at people who complain about TSA security
cnn.com
cnn.com
The things that REALLY keep us safe are pro-active investigations that take place invisibly and silently long before a terrorist gets to the airport.
What happens at the airport, as Bruce Schneier once said, is "security theater." It is an act that makes it seem as though something is being done. It sounds ridiculous, but this is what makes it possible for many people to convince themselves to continue to fly.
Someone who "became visibly upset and arrogantly pointed his finger in the agent's face when asked why he did not have an airline ticket for a return flight." is different than someone who expresses discontent in a non-threatening manner.
The anecdote described by the agent about finger-waving is not in the guidelines. The actual guideline is very loose and will be interpreted by screeners as they see fit and as they see convenient. And they could use it in both situations you described.