They are part of the collection of bolts that secure the outer engine casing in place.
The pressure you experienced was probably due to some oil being trapped in the thread from when the casing was removed/replaced.
This can be bad news if too much oil is trapped in there.
As the bolt is screwed in, it effectively takes on the action of a hydraulic cylinder, compressing the oil. If too much oil is in there, the pressure build up can split the cast aluminium.
It's always worth blowing out any blind threads or using a cotton bud to mop up the oil, before fitting the screws.
Very rarely, even using too much grease on the threads can have a similar effect.
As you experienced pressure, you are OK, no damage has been done. Just make sure the holes are clear before replacing the screws.
As you removed on of them, it's worth torqueing them back down to, just to be on the safe side. 9Nm