Those are real quotes from the game that Hoshi says himself. I always thought Hoshi’s life advices had an important role for his character but for some reason I haven’t seen anyone point out how ironic that a depressed boy had a lot of positive thoughts inside like that. I think that more than showing how sweet he was, it does a nice job in how he secretly still had some bit of hope for life and wanted to live after all (I also like how he warns kaede to not have idealistic thoughts and yet here he’s with how he thinks life is worth it)

source for each quote:

1 - Chapter 1
2- Talent development plan mode, interaction with chihiro (hoshi’s route)
3- Salmon mode
4- Talent development plan mode, interaction with hinata (hoshi’s route)

(Those aren’t all of his motivational quotes in game btw. There is still the interaction with saihara at the beginning chapter 2 and some other in salmon mode for example)