Without the firearm we may never know for sure. My best guess would be that the bolt was gummed up. The mess inside was sticky and thick and it stopped the sear from locking to the trigger. The gummy mess also slowed the firing pin. A disassemble, clean and reassemble would likely have cured it.
I have seen the gummy mess of oil and powder residue slow a firing pin enough to cause misfires, but I'm not sure how it stopped the sear from locking up. Maybe the trigger to sear connection was held open by the crud as well.
Did you oil it with WD-40 ? That gumms up real fast and gets to be like varnish after a while.
You can't fix stupid....however ignorance can be cured through education!