Why does this code not work? Help! How a * (b, c, d) = a??

Question

In a challenge I see:
var x = 7 * (5,7,1);
document.write(x);
My first thought is matrix multiplication or something to do:
(7*5 + 7*7 + 7*1)= 93
But the output returns 7.

I'm not trying to do matrix calculation and get 93, I just want to know how that assignment works in javascript.

https://code.sololearn.com/W0A5BT1DEZ1m/?ref=app