نَأْكُلُ رِزْقَنَا calls food provision from Allah. فَضْلُ رِزْقِ بِلَالٍ فِي الْجَنَّةِ places the fasting guest’s remaining reward in the Hereafter. The statement praises the fast; it does not belittle the host or the guest.
تُسَبِّحُ عِظَامُهُ literally says “his bones glorify Allah”; يَسْتَغْفِرُ لَهُ الْمَلَائِكَةُ says “the angels seek forgiveness for him.” These are unseen matters stated in the narration; they do not require an invented physical or scientific explanation.
The practical lesson joins gratitude for food with respect for someone who is fasting.