Dinah tried to imagine what this encounter must have looked like from Tekla’s point of view. Sean’s arrival was unannounced. Dinah herself hadn’t really known when, or whether, he was going to arrive until the Drop Top had swum into view outside her little window. So, from Tekla’s point of view, this guy was an intruder. And when she’d heard Ivy say "Who the hell are you?" she had realized that his presence on Izzy was completely unauthorized.