That is the technicality by which the ATF lost the case. SCOTUS followed the letter of the law. Congress could change the law to include cyclic rate. M16: 700-800 rds/minute. Bump Stock on an AR-15: 300-800 rds/minute. And, we're discussing how many pulls, or how a trigger is pulled versus . . . Well, not classifying all weapons under NFA.
Congress could do that. But, they don't/won't. No matter whom controls the house. Why is that? </rhetorical question>