Expedia and Google work differently, but this has little to do with "secret" information.
First of all, the main difference is that Expedia is an online travel agent, while Google Flights is a flight search engine.
What that means is that Expedia (or booking.com, or other online agents) will actually sell you the ticket: You pay Expedia, you get the ticket from them, they deal with the airline in the background.
Google flights (or Kayak, or Skyscanner) are search engines. They will collect as much information as possible and show you the cheapest price, but they don't sell tickets. To book you have to go to the airline, to a "normal" travel agent, or to an online agent like Expedia. They often get money from the airline or agent for sending the customer, but they aren't part of the transaction.
This means that Expedia will only show you the prices for tickets they actually sell (they won't tell you if things are cheaper over at booking.com).
Google knows most of the prices, and they have an idea if the ticket is still available, but they cannot guarantee the price. If you try to book from a fare search portal, you'll sometimes find that the cheapest fare isn't available.
Some booking sites, like Expedia, have special deals with the airlines, and can offer tickets cheaper than the "standard" price. Search engines know about those, but not about all of them. These special fares can only be booked through the site that has the deal, obviously.
But remember: If you buy a ticket through an online travel agent, any modifications have to be made through that agent and not directly with the airline. If they sell the ticket extremely cheap, they'll often try to make money elsewhere and may do things things like paid-only customer service or "service charges" for any ticket modifications.
Finally Google flights also shows you fares that are not available online - many other search sites don't, because won't earn money on those transactions.
This is what happened when I tried your search: Google instructed me to call the airline and book the ticket on the phone. It is still possible that the fare is not available when I do or that the airline will calculate taxes and surcharges differently than Google thought they would.
Finally, if you use Expedia or such sites, it is always worth to try and search for "Hotel+Flight" - in some cases that combination can be cheaper than the flight alone.