وَإِنْ مَاتَ عَلَى فِرَاشِهِ means “even if they die in their bed.” The apparent ordinariness of the outward situation is contrasted with the promise of lofty reward; true intention may matter beyond what others observe.
مَنَازِلَ الشُّهَدَاءِ is an iḍāfah (construct) expression meaning “the ranks of the martyrs.” The report does not authorize certainty about any named person’s unseen intention; Allah knows what is in hearts.
The practical focus is truthful prayer, faithful fulfillment of duties, and goodwill toward others.