Any personal foul is an automatic first down. This is an NFL rule and not necessarily applicable to lower levels.
On a tangent - you are right it doesn't make sense. So you have misconduct personal fouls like a flagrant face mask, late hit, spearing, hitting a defenseless WR with helmet or whatever. These are all 15 yards. It is also understandable that these get an automatic first down because basically most of these are so egregious that it should be more than 15 yards but that has always been the max penalty doled out...
So why have a 5 yard penalty for hands to the face when you are basically saying - "that guy had his hands on the face of the other guy but didn't seem to be doing so on purpose and didn't seem to be trying to hurt the other player" AND then give them a first down. That doesn't make sense. To step in line with other penalties it should be a "free-play" for the offense and then 5 yards and repeat the down which is still a hefty penalty given the free-play status.