Incidentally, I simply do not believe that downwash of itself can set off an anti-personnel mine. Debris blown onto a mine, possibly.
Some AP mines have little prongs that protrude just above the surface, and only need the slightest touch to set them off. The prongs can be connected with tripwires to increase the likelihood of someone setting them off. So, yes, the debris kicked up by a helo could easily set one off.