Sorry, no. It’s just sloppy writing.
In a classical interferometer, first developed in the late 1800s, a laser beam in a vacuum hits a mirror called a beamsplitter, which breaks it in two. The two beams travel at different angles down the length of two vacuum pipe arms before hitting mirrors at the end and bouncing back to the beamsplitter.
Since the LASER wasn’t invented until 1960, late 19th century interferometers used a very bright, but non-coherent light source.
This gives me a chance to mention my favorite experiment of all time, the Michelson–Morley experiment. Michelson actually invented the interferometer to measure the flow of aether. The scientific consensus of the late 19th century was that light waves traveled through aether just like sound waves travel through matter. The experiment failed to detect aether and is now known as the most famous failed experiment in history.
So much for consensus.