The Germans layed mines and booby traps at an alarming rate from 1943 till the end of the war, especially in the West.
In addition, this is a critical part of TGD and any German player not fully utilizing his engineers in this capacity will lose fast.
Minefields are pretty clearly minefields in TGD. Not booby traps or obstacles. The fact that they are on the board at game start and that your friendly units can freely move through them indicates that.
There is a disconnect between the games in the series as well. Did the German/British/American engineers not have mines in the other games?
As I said previously, considering the scale of the game, mines were represented well by rear guards/roadblocks/entrenchments.