Shooting at ISO400 and 1/250 f/5.6 seems OK if there was bright light "outdoors", so here are some options:
1. You think those were the settings, but accidentally there were changes from those settings, and film was underexposed.
2. A meter problem (not usual) and film was underexposed.
3. A development problem (time/temperature/contamination)
4. A scanning problem (not usual) but film is fine.
or
5. The scene required more light than 1/250 f/5.6, but some external (brighter) light made the meter guess less light was required, and the man, the real scene -that looks several stops below external light- was underexposed.
Cheers,
Juan