No, it was set to new_id (L 754 in old code). usage_id was just used to create the query string. It created 
{'$set': {'blocks.<usage_id>.edit_info.update_version': new_id, 'blocks.<parent_usage_id>.edit_info.update_version': new_id}} which is passed to .update({'_id': new_id}, the_above_dict)) after doing the insert. This code computes new_id locally rather than via .insert and thus can set the value before the insert rather than as fixup after the insert.