The Kraken is originally from Scandinavian folklore. However, besides Clash of Titans (where the kraken doesn't really look like how we usually see it depicted), the Kraken is also associated with the Greeks in Age of Mythology and in Theros, the Magic setting. Did Clash of Titans invent this connection or did it already exist? If the latter, where did it come from? If the former, does anyone know where they got the connection?
The term "kraken" is from Scandinavia, but that does not give Scandinavia exclusive claim to being the origin of all sea monsters. Belief in and legends/myths about sea monsters are ubiquitous. The Greek word for these sorts of creatures is Ketos/Cetus, and their place in Greek oral tradition is attested to by ancient documents including those preserving the stories of Perseus and Herakles.
The existence of sea monster traditions in various cultures does not imply historical connections; nor should we exclude that possibility. The Indo-European inheritance of oral narratives appears to have included these sorts of monsters, described by various names, and that may be the source for similar myths in Scandinavia and ancient Greece. That said, I'm not prepared to stand on that assertion, which would be extremely difficult to prove.
The choices of various modern media presentations to employ the term "kraken" out of context is something that those writers could explain. It is clearly out of place, but one must admit that "kraken" has a lot of bite to it, where "Ketos," as a word, ends with a whimper. That may be sufficient to explain the importation of the Scandinavian word.