That's based on a misleading "fact." Many people claim that most victims of homicide knew their killer. That's true only when the relationship between the two was known. The most common relationship, by far, is "relationship unknown". [1] You are much more likely to be killed by a stranger or somebody who is "relationship unknown" than anybody else.

And furthermore most gun crime is committed by people who do not legally own the firearm being used. [2] I'm loathe to link to that site, but this is an issue that is poorly reported and so it requires exploring a web of data sources, which they actually competently do, on this issue at least.

You can also kind of sniff test this claim by considering that homicide rates are much higher in urban than rural areas, yet urban areas have dramatically lower gun ownership rates.

[1] - https://cde.ucr.cjis.gov/LATEST/webapp/#/pages/explorer/crim...

[2] - https://www.politifact.com/factchecks/2018/mar/12/john-faso/...