en.wikipedia.org/wiki/2017_Las_Vegas_shooting

This clause misstates what the federal rule actually did.

The Justice Department's 2018 final rule said that bump stocks / bump-stock-type devices fell within the regulatory definition of a "machinegun." It did not say that rifles equipped with bump stocks were themselves reclassified as machine guns.

That distinction matters because the Supreme Court later described the rule the same way: ATF had issued a rule "that classifies a bump stock as a 'machinegun'" and the Court held ATF exceeded its authority in doing so. The Court further held that "[a] semiautomatic rifle equipped with a bump stock is not a 'machinegun'" under the statute.

So saying the ban was enacted by "classifying rifles with bump stocks as machine guns" is legally inaccurate; the rule classified the device, and the Court later rejected treating a semiautomatic rifle with a bump stock as a machinegun under the law.