Later in the speech Alexander returns to this theme to sum up his characterization of the kind of man he sees himself as being and wants his men to be, as well:
A. B. Bosworth, the most prominent recent scholar of Arrian’s account of Alexander, suggests in his discussion of the speeches in Arrian that, although this particular passage probably depends on the contemporary source Ptolemy, these sentiments are not genuinely Alexander’s thoughts but rather reflect the oratorical training of Arrian’s time: “the topos supports Arrian’s flight of rhetoric in V.26, which culminates in the proud claim that a life of hardship for virtuous ends is pleasant in itself and the guarantee of immortality. It was a grossly inappropriate theme to air before officers and men who were soaked, exhausted, and weary with the endless pursuit of glory. Alexander may have been insensitive enough to enlarge upon it in such a bombastic fashion, but we cannot assume it. The evidence so far adduced suggests that the rhetoric is Arrian’s and is more influenced by the declamations of the schools than by the immediate historical context.”  The evidence that Bosworth adduces here comes first of all from remarks that the elder Seneca makes about Roman declamations concerning Alexander (Suasoriae 1), but Bosworth also refers to Thucydides (1.23) and Xenophon (Cyropaedia 7.5.80). He does not cite Homer.
Aristotle’s argument here is well explained by William M. A. Grimaldi, S.J.:
This conclusion is in fact supported by what Aristotle says about the diversity of character observed in animals:
The philosopher’s culminating point here on the difference between being well born and being noble sums up what Alexander would have learned from Aristotle about what it meant to be a “noble man” (γενναῖος ἀνήρ).
The speaker here is Diomedes, replying to his comrade Sthenelus, who has urged Diomedes to turn back now that he must face a more formidable enemy in the duo of the archer Pandarus and the warrior Aeneas. Athena had given Diomedes “strength from your father” (5.125: μένος πατρώϊον); Diomedes emphatically tells Sthenelus that if they can capture the special horses pulling Aeneas’s chariot, they will win “distinguished fame” (κλέος ἐσθλόν).
These passages make it clear that the sentiments at Anabasis 5.26.1 and 5.26.4—a “noble man” would not turn back from the challenge of going beyond the Hyphasis River to face even the most dangerous of enemies, that his spirit and strength would drive him to “go beyond,” and that the reward for his taking action would be “undying fame,” the kind of fame that turned a man into a god—are perfectly “true and appropriate to the speaker,” to Alexander the “man who loved Homer.” Indeed, the sentiments, even the very words themselves, are so true and appropriate that it is tempting to speculate that they in fact do go back to what Alexander actually said in his speech.