Can you tell me where you read that rule?
See the reference guide at the bottom of page 4
Combat with a vampire encounter can occur when either a hunter resolves a search action or Dracula ambushes a hunter.
» Combat with an “Aggressive Vampire” can only occur with one hunter while combat with a “New Vampire” can occur with multiple hunters in the same location if other hunters at that location become delayed.
Note that this mentions an "Agressive Vampire". The official FAQ, confirms it should say "Reckless Vampire".