What is the meaning of "static pressure"?
There is a static pressure port, often on the side of the aircraft, that senses the air pressure at the altitude the aircraft is flying and unaffected by the aircraft's passage through the air.

The pitot tube, facing into the relative wind caused by the aircraft's passage through the air, measures the ram air pressure, which is higher the faster you go.

The indicated airspeed is the difference between the ram air pressure and the static pressure, subject to some adjustment due to sensor positioning.

The altimeter operates off the static air pressure.

So, if the static line is somehow opened to the inside of a pressurized cabin, the system will read that higher pressure and believe the altitude is what it is inside the pressurized cabin, which will be significantly less than the actual altitude.

And the difference between the ram air pressure and the false higher static pressure (the pressure inside the cabin) will be much less and the system will read this reduced different as a much lower speed.

This is a somewhat simplified answer.