A technicality is a trivial or very small detail. You might consider your scuffed, unpolished shoes to be an unimportant technicality when you're dressing for a job interview.

What does it mean to get off on a technicality?

To "get off" in this context means that they were allowed to go free, without facing any charge/punishment. A "technicality" in this instance means that they got off due to something which meant that their trial could not take place properly because of an error, or a problem with the system itself.

What does it mean to be technical?

In short someone that is technical is skillful. They do not have any of the markers of energy inefficiency or use of extreme physical qualities like strength, explosiveness, speed, or flexibility without the presence of specific form. That means their movements have purpose, direction, and produce a positive result.