I explained what the event you created does..
If you want it to do anything different, you should change the event..
You could solve it by by:
on spacebar pressed
bullet set angle of motion..
on bullet created
bullet set angle of motion
or any other event referencing the bullet you want to affect..
Right now there is no reference to the bullet, so all bullets are affected.
By placing it under the create action, the bullet in the next line is the one just created..
By using the on created event, you are referencing the bullet..