Upvote:4
If the flight is with Swissair and you can't book it with Swissair, you can assume there is no flight. Or does Swissair have the flight, but not at the price advertised?
The flight and price quite possibly existed at some point. This is implied by the same flight on dates in April, May and June being available at as little as 513 USD, now, as well as them being bookable through United.
Here's an example link (which will probably expire):
Hipmunk lists the flight you searched for at about 1000 USD:
Momondo offers that flight for about 860 euros:
So, you likely found old flight data.