You're still assuming that homicides are replacing assaults.

That's one possible explanation, but there isn't nearly enough information in the chart above to conclude that. An alternative explanation could just be that Covid made people stay inside, and that assaults happen more to strangers on the street while homicide happens more often between people who know each other and who spend lots of time together indoors.

Spending more time indoors could explain those trends just as easily as increased gun ownership. There isn't enough info in the chart above to tell which of those factors is having an impact.