Angry old customer threatening to get me fired

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I work at a retail store and a customer threatened to talk to my manager and get me fired. He said this after I "cut him off" by walking past his mobility scooter out the door and made him veer left into a rail and cut his knee.

A couple of things with this in my defense:
>he "crashed" into the rail at least a good 3 seconds after I passed by him
>the angle at which he would have had to swerve out of the way was the wrong one, there is no way I could pass him by on his left side and he would swerve to the left to avoid me and bang his left knee

He didn't report anything in today at all, but he was an old man who seemed the type to try and JUST my shit up when he can, so I'm expecting him to come back.

What should I do? The thing is, the angle at which he would have had to s right now and I'm still on my probationary period there. This basically means that they can fire me immediately if my work is no satisfactory.

Pic unrelated. I think I have a good case in my defense but it ultimately comes down to how the security footage appears, what should I do?