Labor theory of value claims that the value of X depends only on the amount of labor required to produce X. This theory doesn't explain how gold is more valuable than iron, or how $UNICORN is more valuable then this other startup. So it's a bad theory.

matthewowen's argument is not assuming the labor theory of value is true. It's just pointing out that, other things being equal, if the demand for X increases then the demand for X-makers' labor increases too; hence X-makers' wages increase.