Could the
row-order have changed when doing COPY FROM with pg_restore?
There is no reliable, meaningful, row ordering when it comes to the physical files. Sure, cluster does make an attempt, but it is quite limited in practice.
A *logical* dump of data shouldn't be affected by on-disk order.
Internal representation shouldn't affect the output.
The logical dump has no ordering - it will come out however it comes out. "COPY <table> TO ..." doesn't have an order by clause - there is no way to make or communicate to it that ordering is important.