Men do commit nearly all of the violent crimes against strangers, but women commit violence against acquaintances at roughly similar rates to men. My impression is that violence against strangers has decreased quite a bit over the last couple of decades but that domestic violence has remained steady, so I'd expect that graph based on composition effects.

I suspect that the gap in murder rates is higher since due to size differences random male on female violence is more likely to be fatal than vice versa. For instance a male acquaintance of mine's ex-girlfriend snuck into his room at night and stabbed him, but thankfully she wasn't able to get the knife through his ribcage and he lived. If the genders had been reversed it might very well have gone differently.

Your acquintance really lucked out. I think his case was an outlier. Rates of murder in countries with and without guns are pretty much the same because the barrier is not the tools. It's fairly easy to kill with any tools. The only thing that saves us from being mudered are mental blocks against murdering tht almost all people have in their brains.