Yep, "sou (desu) ka" it is. 'Sokka', for short.
The 'ka' particle isn't really meant to make it a question, btw. It's like the German: "Ach so!?" Hence, when I encounter "Sou ka!" in Anime, I translate internally to "I see!" (which is pretty much short for "O, it's like that?! I see!"). There's a built-in realization moment, as it were, followed by the statement that you (now) understand. It's not just the same as wakarimasu! (also "I understand")