Congratulations Miriam, Saamuel, Hannes, Kadi, Jael, Hedi, Tuudur, Merle, Peep-Reimo, and Tuuliki!
This is a very common style of slab foundation in Estonia now, though the use of factory-cut foam blocks was new to me. We have shifty, wet soil here and with cold winter temperatures, frost-heave can cause real issues for standard footer-form style foundations.
So instead they pour a reinforced slab which sits on top of a bed of compacted gravel, sand and high-density foam insulation. Floor-heating pipes are laid in contours according to the interior wall layout and then concrete is poured to form the slab. Notice in the picture of the wet cement the small metal filaments included in the mud that provide additional resiliance.