Mathematically, it means that the number of lines read is bounded by 10*M, where M is some constant. So it's basically equivalent to saying that it's O(1).
I'm guessing that intention was to say "around 10 lines", though it kind of stretches the definition if we're being picky.
Proportionality is at the center of defining a war crime.
"The principle of proportionality (Article 51(5) (b) API) states that even if there is a clear military target it is not possible to attack it if the expected harm to civilians, or civilian property, is excessive in relation to the expected military advantage."
So, the case that Israel has to make here is that the expected millitary advantage from the operation exceeds the collateral damage. The fact that civilians died doesn't automatically make it a war crime from an international law point of view.