Sounds like one side of the seat recliner moved without the other. You need to disconnect the cable from one side of the seat where it connects with either the motor or the worm drive on the seat mechanism. Then, when you operate the power seat only one side will move and you can realign it and then reconnect the other cable.
If that isn't what it is, he could have bent the seat frame. I've never heard of this happening on an E34. I'm a pretty big guy too and my seat is fine.