That is true though in the chronology, Gerdal leaves on the Snake-men trip on May 28th and Sven interrogates the Soothsayer on May 21st. So technically you are both still in Helix at the same time.She did! But alas, she is in the forest looking for snakemen right now.
I am fine with players interacting between each other, engaging in tavern conversations. You just obviously can't make a decision or action that impacts what you are committed too as a future event. (For example we know some folk go to Ironguard so obviously they can't also join another trip that leaves the village before they return).