That's because comma is a language construct, which acts like a semicolon that waits for all operands to finish before returning the last value returned.

The comma operator evaluates each of its operands (from left to right) and returns the value of the last operand.

Since the last statement to finish returns false, the result of the whole operation is false.

const foo = typeof true, false;
console.log(foo);

// could be re-written as

const _ = typeof true; // not used
const foo = false;
console.log(foo);


// another example: bar will contain false!
const bar = 'a', 3, true, {}, Symbol(), false;

Reference: MDN