It was implicit also elsewhere, in many other sentences. Possessive being implicit in Latin seems common.
Romance languages tends to be more implicit regarding pronouns than English (not only subject-pronouns, but also possessive).
From this page:
"It's implicit. Possessive pronouns are only used emphatically : suus = one's own."
(I think they are also used when there's a possible ambiguity)
It could very well be a bunch of mates that he doesn’t know. Example: Marcus was travelling from Rome. On the evening of his first day of travel, he came upon a group of men and they agreed to come together. Markus doesn’t have much food with him, so they will share his food with him if he stays up during the night keeping watch, and wakes them up early in the morning, as they have to get going quickly. They are tentbuddies from the army, and not his own buddies. Marcus wakes the comrades up in the morning.