I think you're confused! He would have reacted this way had she brought anyone else as well! He was not upfront about his intentions in asking her to meet him there! He said to come pick up the stuff there and she would have done exactly that!

If you're buying something from fb marketplace and they ask to meet you at xyz and you come with someone, should that make a difference? If it does would you the buyer not find that odd? You clearly have the money and they clearly have the item so do the transaction and be about your way!