Why was he wandering the streets?

Without more specific context about who "he" is, this is tough to answer definitively. People wander streets for countless reasons - some might be lost or disoriented, others could be experiencing homelessness, some might be exercising or walking with purpose, and unfortunately, some could be dealing with mental health challenges that make being indoors difficult. If you're concerned about someone's safety, the kindest thing might be to check if they need help or contact local services who can assist them properly.