In the image, Sophia and Dylan are near the whirlpool and therefore can see it well. Sophia's expression looks surprised and amused at the same time, while Dylan looks pleased with himself. Dylan pitched the hot tub so if there was a problem with not being able to use the tub, Dylan should look disappointed or pissed. In my opinion, while Sophia was getting ready to go out, Dylan prepared a surprise for his mother, for example a romantic dinner immersed in water with glasses and candles. So Dylan surely knew what they were going to find, hence his pleased expression on him to see his mother surprised.