The Reuters article has it correctly with the necessary qualifier, Swiss Complete World’s Longest Rail Tunnel.

They fail to mention the 4 other tunnels that are quite a bit longer than the Swiss tunnel.

If you believe Wikipedia, see their article, List of longest tunnels in the world. The longest one is 85 miles compared to the puny Swiss tunnel of only 35.5 miles.

Of course, if you go by volume, perhaps the Swiss tunnel does have some bragging rights.  I don’t know the numbers for this measure.