From the available information
a) what makes you think the documents were very good fakes or 'legit fake' identities (whatever you mean by that last one)?
b) what gives you reason to believe the documents found on him weren't genuine (just not enough to grant admission to the US)?
c) what makes you think either the Russian or the Israeli authorities searched databases looking for a booked ticket?

In the press this morning (Berlingske):

The passenger was Sergej Ochigava, 46 years old. Arrived by Metro at the airport. Without a boarding card, he got through the gates to security by following another passenger. Then, at passport control for entering the non-Schengen area, he was stopped due to not having a boarding card, and his passport was taken for checking. He was ordered to sit down on a bench and wait. At some point he gave up waiting and somehow entered the area anyway. Then, same night, he tried to board SAS flight to Bangkok by presenting Russian ID and a note written in Russian. He got rejected. Next morning he tried a flight to London, but got rejected. A little later, he lined up for boarding a SAS flight to LA. He got on board by going through the boarding gate with a family with three children. He went to business class, where staff tried to talk to him. He didn't reply and went into economy and found a vacant seat. The plane took off. During the flight he had multiple conversations with crew, and changed seats multiple times, and thus managed to get food served multiple times. He also obtained some chocolate belonging to the crew. Upon landing in LA, he small-talked with another passenger and they exchanged phone numbers. He then contacted ground staff and told them he'd lost his passport on the plane. The aircraft was searched with no luck. He got detained and searched, which produced a Russian and an Israeli ID card. The next day FBI arrested him.

According to New York times he has a PhD in economics and marketing, and worked with that in Russia. His phone was a picture of Copenhagen airport, a screenshot of Google Maps showing a hostel in Kiel, Germany and a map showing an unknown town. He risks 5 years in prison.

According to the article security has been tightened so won't happen again :-)

I don't understand laws that put such trespassers in prison.
Expulsing them make sense. Keeping them in administrative custody until expulsion make sense.
Fining them and freezing whatever asset they have for paying the incurred costs make sense.
But in what way will putting them behind bars protect the public and make the society more secure?
Such laws looks to be made for punishing rather than made for protecting and organising.
Is that civilisation?
That baffles me.

One could even argue there is a value in behaviour like this. He has demonstrated weaknesses of the system without any violence or actual bad intention. Who would have expected this to be possible? Aside from what he did, he sounds more like being in need of some psychological support instead of a prison cell.

If you do not understand, .... just follow the money. So, who will profit from having him in prison for years?
Answer: U.S. prison industry. More people are booked in, longer the sentences, more public money towards businesses, running the prisons.
https://www.sentencingproject.org/re...united-states/
Totally agree, serving 5 years is out of touch of anything civilized. Would that mean that any immigrant, illegally crossing the border into U.S. shall be sentenced the same?

It looks more that this guy needs psychological treatment and/or expulsion at the expense of the airline that brought him in.