Yea... you got lucky too.
Look up a picture of a new one and you'll see how they attach... a screw in the centre that pulls on a wing nut.
To remove, loosen the screw as much as it will go and then pry out the old block heater... usually have to twist it sideways as the heater loop sticks down a bit. I find it easiest to work from under the engine.
Clean the hole carefully, install a new heater, tighten it up, and away you go.
BTW, I can't recommend Canadian Tire one-size-fits-many blockheaters... given how much of a pain it is when they blow I'm convinced it's worth the trouble to track down an OEM one... almost the same price anyways and exactly the right size.
Way to dodge a bullet !!
Vince