How can a car have 0 compression in a cylinder, but have enough pressure to blow off a spark plug wire without the plug inside?

Supposidly I have 0 compression, but you can't put your hand over the hole without it blowing it away.

 

broken compression tester?

 

That''s what I'm guessing, because in order for that to happen there has to be compression right?

 

yeap

Even if you didn't have any rings on the piston, at the speed of just cranking it would still blow out a good poof of air at you through the spark plug hole