No, the sear replacement is a 10 minute job for an experanced armour.
If the gun was “gummed up” why would he tell the nieghbor not to push the selector level past semi?
I spent 22+ years in the service, 10 years as an Air Force Security Policeman working in the armory with M16s, M4’s SAW and every weapon they had.
Trust me, this was no malfunction.
The one in this guys rifle apparently did. This in no way means he modified the rifle for full auto. It was a MALFUNCTION.
And this guy is now a felon because of an over-zealous out of control rogue agency that has no Constitutional authority to exist in the first place.