The WP has the report here:
On Thursday evening, a 40-year-old man — with dark, curly hair, olive skin and an exotic foreign accent — boarded a plane. It was a regional jet making a short, uneventful hop from Philadelphia to nearby Syracuse.
Or so dozens of unsuspecting passengers thought.
The curly-haired man tried to keep to himself, intently if inscrutably scribbling on a notepad he’d brought aboard. His seatmate, a blond-haired, 30-something woman sporting flip-flops and a red tote bag, looked him over. He was wearing navy Diesel jeans and a red Lacoste sweater – a look he would later describe as “simple elegance” – but something about him didn’t seem right to her.
She decided to try out some small talk. Is Syracuse home? She asked. No, he replied curtly.
He similarly deflected further questions. He appeared laser-focused — perhaps too laser-focused — on the task at hand, those strange scribblings.
Rebuffed, the woman began reading her book. Or pretending to read, anyway. Shortly after boarding had finished, she flagged down a flight attendant and handed that crew-member a note of her own.
… this quick-thinking traveler had Seen Something, and so she had Said Something.
That Something she’d seen had been her seatmate’s cryptic notes, scrawled in a script she didn’t recognize. Maybe it was code, or some foreign lettering, possibly the details of a plot to destroy the dozens of innocent lives aboard American Airlines Flight 3950. She may have felt it her duty to alert the authorities just to be safe. The curly-haired man was, the agent informed him politely, suspected of terrorism.
The curly-haired man laughed. He laughed because those scribbles weren’t Arabic, or another foreign language, or even some special secret terrorist code. They were math. Yes, math. A differential equation, to be exact.
Had the crew or security members perhaps quickly googled this good-natured, bespectacled passenger before waylaying everyone for several hours, they might have learned that he — Guido Menzio — is a young but decorated Ivy League economist. And that he’s best known for his relatively technical work on search theory, which helped earn him a tenured associate professorship at the University of Pennsylvania as well as stints at Princeton and Stanford’s Hoover Institution.