Williams didn't "escalate it". Williams brought to an end an attempted armed robbery. If you don't believe that Williams' actions were warranted, then you'll probably find yourself among a small minority who share your opinion.
Everyone's entitled an opinion, including me.
Williams said that he thought the robbers would start shooting. The news article doesn't say why he thought that. However, I saw nothing on that video that indicated that the one perp with a gun was threatening to shoot anyone. When confronted by Williams, he ran like a rabbit.
Yes, Williams deserves credit for stopping a robbery. But, in doing so, he fired a shot at the perp while one, and possibly two other innocent bystanders were in his field of fire. And two patrons were also between him and a possibly armed accomplice.
It all ended well, at least for now. Hopefully, an anti-gun DA doesn't decide to harass Williams for continuing to shoot after the perps had fled the premises. I don't know if FL law allows the use of deadly force against a fleeing felon.
But, it could have very easily all gone bad, and Williams would have been blamed (rightly or wrongly) for escalating the confrontation. As someone else posted... it's really is a difficult choice: if you act preemptively, you risk making the situation worse. But, the only way you can be sure is to wait until the perp actually shoots someone.