Hate to break it to you guys, but the person who gets the killing blow gets the toolkit to disarm the mine in the next field. However, I'm still not sure how the title is handed out. The person running the controls up top got it in our run, and I got it myself. However, the tank who also got a few killing blows and disarmed some, did not get the title. Also the person who disabled the field just before the boss fight didn't either.
No, no, and no. I am a healer. I wanted the title, so I stood under a few probes while healing people. I did zero damage. I got the kit, defused the mine, and later got the title. It is proximity alone, period.