but this particular reading of the statute essentially renders it moot and devoid of any sense. Interpreting the statute as the judge has basically means that if Kyle was wielding nunchucks instead of an assault rifle, the charge would've stood (because of the confusing short-barrel language of the statute).

The judge knows his interpretation swallows the statute whole and makes it useless.

So no - it wasn't technically incorrect for the judge to read the statute the way he did, but it was awfully convenient for the defendant, whom the judge clearly has affinity for.