Surprised it fired. I let a friend load magazines and he ended up using .223 in one and tried firing it out of my Vz 58. The cartridge got stuck. First and last time I let anyone load my mags, experience be damned.
Sounds like a missed learning experience for your friend.
Why did YOU let him load YOUR mags into YOUR gun ?
Was the .223 beside the 7.62x39 ?
Friends teach friends how to load mags and guns safely.