[lainga]

It is cyber in the sense of cybernetics ("the mathematical study of communication and control in the animal and the machine")

[kazinator]

Let's see:

https://www.etymonline.com/word/cybernetic#etymonline_v_3657...

"kybernetikos": Greek for "good at steering".

Thus military attack involving an excellent steering maneuver is cyber attack.

[Udik]

Not too sure about the -tikos thing and the "good at" part, google (and the Oxford dictionary) gives etymology from kubernetes, pilot. Cybernetics is then, I guess, the science of (automatic) control, so nothing to do with "steering".