That’s not a kingmaker
A Kingmaker is a player who is incapable of winning, but can still influence which other faction wins (in many important instances they decide which faction wins). In some rare cases involving Survivors, a Kingmaker might be guaranteed to win, instead of incapable of winning.
Kingmakers are generally unwanted in game design. For this reason, most third-party players who cannot possibly fulfill their Win Condition simply leave the game.
Strigoi, in a majority of cases, is neither incapable of winning or incapable of losing
Special case scenarios where this is not the case
- Last scum/town left alive is going to die very soon (wincons immediately going to be reached regardless of what Strigoi can do. In this case Strigoi optimally tries to play to its wincon
- Strigoi has mostly everyone infected.
Strigoi is, for all intents and purposes, an unlyncher with everyone it bites as targets.
It is always efficient to side with the players it has bitten, making it similar to a Merc