why do not look into optimizer_mode parameter.

If it is CHOOSE, FIRST_ROWS, ALL_ROWS then most probably CBO is employed (unless querie's hint overrides it)

If CBO is used, then statistics are important and must be checked if still available after moving table to new tablespace -> best of all if they are exactly the same as were before reorganization.
Creating new/modifying existing statistics can even make things worth.

Just for fun, if indexes are available and non CBO specific features are used(like partition pruning), try to set optimizer_mode=RULE