You ran DBUTLTY BACKUP DBID=700,SEQ=NATIVE.
This native sequence backup uses the Native Key defined to each table in a data area to reorganize the data area in Native Key sequence.
This ENF area uses DSOP MODE - SEQUENTIAL .
With this mode , deleted row space is not reclaimed until you run a native backup/load .
So when you use this backup as input to the DBUTLTY LOAD function , each row will be reloaded in perfect native key sequence .
DBUTLTY reloads the rows in each data area block until it is completely full . When the load finishes , the number of used blocks can be lower if the data area blocks had space that was not reused for deleted rows.
Before the load , the data took BLOCKS IN USE - 1,262 per your CXX report and after the load BLOCKS IN USE - 87 .