I think this picture will explain the problem.
<picture>
It's hard to see, but the achievement clearly say "Kill 150 people with remote mines", but in progression bar, it's 1/50...
Also, Boris isn't invincible at all : I was supposed to got this achievement yesterday but nothing hapenned... I think there's a problem over here.
I think that is a typo of some sort.
No no no no no... it was here BEFORE I changed the translation.