Thought So
This person did the polite thing by asking their friend whether they would be busy on Valentine’s Day. The OP didn’t have a Valentine’s date and told them. The reply was the best kind of savagery: accidental. They actually started their asking for a favor with a “thought so.”
You already knew that this person wouldn’t have a date on Valentine’s Day? What’s worse is that this person wasn’t even going to ask them to be theirs! They needed a favor from the OP, knowing full-well that they’d have the time because she was painfully single. This is what struggling really looks like.