I have a theory that the game unintentionally gives you a stalker of sorts in the form of the Sim you first make contact with. Johnny Zest as one of the most likely Welcome Wagon candidates is a great example. Anyway, this Sim seems to be the one constantly ringing up to invite out. Festivals included.
Random side question; but somewhat related to the topic at hand: Can Sims just get “spur of the moment” married at the Romance Festival or do they need to be engaged first?