He was in a shooting position, similar to this
With the way his shoulder was shown to be in the next panel in order for him to achieve that position he had to have to have
at least taken a step, there is no 2 ways about it
You can even try it yourself, try moving your shoulder in this same position, you can't simply move your shoulders alone without taking a step back
That's like, all the evidence needed, explicit evidence isn't always needed, it's not like you need to see the dog to determine a human was bitten by it even when
1 the very spot where the human was bitten is there
2 you know how a dog bite looks like
3 The Bite looks exactly like 2
What you're asserting is no different from asking to see footage of the individual being bitten for you to actually confirm he was
If there is a problem with the analogy do Say it
Gotta go now, see ya