> The TSA detained the man (possibly illegally)

Not 100% sure that it was illegal. If you walk out of a retail store and set off those alarms, they do not have the right to search you. They do have the right to detain you iff they are holding you for the cops to get there (it becomes illegal when they detain you without calling the cops). This can vary from jurisdiction to jurisdiction, but in general I believe this holds true.

Though I believe that the TSA should be held to a higher standard in their jobs (retail employees/managers are not trained to deal with this sorts of issues, at least not well).

I'd say "unreasonable" is not answering the reasonable, banal questions of people employed to protect travellers and the nation at large.

Protect from what? Cash isn't a threat and it isn't contraband. $5k is only half of what it takes to raise bankers' eyebrows, and they're at least qualified to investigate money laundering. The TSA goons had no defensible reason to waste this guy's time, much less go on a fishing expedition into what's usually intensely personal affairs.