Was what I did correct, or is ghusl (ritual bath) required of me after discharge containing a spot of blood before sleep and waking up before Fajr (dawn prayer) and performing istinja (cleansing after defecation/urination) without checking the area, knowing that my clothes were clean, and upon checking the area an hour later I found dryness, then performed wudu (ablution) and prayed Fajr? And was I required to check the area before performing istinja?

What you did is correct, and you are not required to perform ghusl (ritual bath); because what you saw is not considered menstruation according to the majority of scholars, and this is the fatwa given, as the minimum duration of menstruation according to them is one day and one night. Even if it were blood, you are only required to perform istinja' (washing private parts) and wudu' (ablution) before prayer, and there is no harm in not inspecting the area before istinja' because the default assumption is that nothing else has exited.