I don't know if adiabatic processes are responsible for the temperatures in the core, but if it is, it would be more accurate to describe this in the past tense, rather than the present tense that the other commenter used:

>"High pressure makes made the core hot"

You made the same distinction:

>the earth was pressurised

That being said, I doubt adiabatic heating plays a significant role. Adiabatic processes operate through compression, not pressurization.

Suppose I have a sealed tank of water. I put a balloon inside it. Then I pressurize the water to double the pressure in the tank. The volume of the balloon shrinks.

Here's the important part: Even though the balloon is half the size now, it still has the same amount of heat: none has entered or exited yet. The same amount of heat in a smaller volume means the temperature has risen. That's adiabatic heating.

Replace the balloon with an iron or nickel ball. When you double the pressure, the volume of the ball doesn't change. Increase the pressure a hundred times, a thousand times, it doesn't matter: the volume of the ball stays the same. The heat within the ball is not concentrated. There is no adiabatic process involved.

With the core of the earth being primarily comprised of non-compressible materials, I don't think adiabatic heating explains the temperature of the core.