metaphor.
Yes, "He was part of the morning fog" is a metaphorical expression. It suggests that like the morning fog, he was mysterious, fleeting, and intangible.
A metaphor for fog could be a "veil of mystery" or a "blanket of uncertainty" that obscures clarity and vision.
fog moves silently
A graveyard is fog.
What type of cloud that is often formed by fog lifting in the morning?
There is least chance of fog or mist in the morning as the water vapor present in the atmosphere sheds in the form of rain in the evening and results in least chance for fog or mist in the morning.
Morning
stratus
yes
Morning
stratus
The Morning Fog - 2006 was released on: USA: 2 November 2006 (Indo-American Arts Council Film Festival)
............. was as clear as fresh morning dew