Yes he is adding water
"Whereas in the "test tube within a bottle" method, the 1.5 grams of malic acid powder is diluted less, since the test tube the malic acid powder is placed in is only about 50 ml in volume. Thus it becomes a stronger acid in that smaller volume. Even with cold water and just one rod, I find you get a pretty vigorous reaction going on inside the test tube."
"Whereas in the "test tube within a bottle" method, the 1.5 grams of malic acid powder is diluted less, since the test tube the malic acid powder is placed in is only about 50 ml in volume. Thus it becomes a stronger acid in that smaller volume. Even with cold water and just one rod, I find you get a pretty vigorous reaction going on inside the test tube."