Gobbledegook and balderdash
Forget all this silly and unscientific stuff about interactions with the solar field and the suggestion of a "core plasma"
We know that planets are heated by internal radioctive decay, and this obviously diminishes with time.
We also know that as part of the planetary formation process, compression, collision, and coalescence occur - with associated heating.
So planets form warm, and then cool.
but be very careful about SURFACE and INTERNAL heat.
Surface temperature depends on solar flux and atmospheric greenhouse effect.
Internal heat depends essentially on heat-of-formation and radioactive decay.
Surface temperature mediates the options for life-as-we-know-it.
Internal temperature mediates volcanism and tectonics and the "deep dark biosphere"