During that period travel to Pakistan by US Citizens was prohibited by The State Department, so he couldn’t have used a US passport. Besides, this was during the period he was claiming to be an Indonesian national. His “citizenship” and national “loyalty” has always been very fluid.
“During that period travel to Pakistan by US Citizens was prohibited by The State Department...”
That is complete nonsense as at that time in 1981 and at all times since then, Americans could enter Pakistan.
Here the NYT published a piece regarding travel to Pakistan in the summer of 1981.