If your son wasn’t sure, why didn’t he write the notes down anyway since they were already in his head? Then he would’ve covered all his bases - would’ve had the assignment ready to turn in in case that’s what she asked for but also had the possibility of doing a makeup assignment.
If the teacher’s policy is normally that you turn in work on the day you return, then that should’ve been what he prepared. Even if she’s sometimes “known” to give out makeup assignments, if that’s not an every-time thing - and also not the classroom policy - he shouldn’t have relied on that as a possibility. He should’ve had the assignment itself prepared to go.