How to make tofu that is crispy and flavorful outside and soft inside?
Most likely, they are using a softer tofu than you.

For whatever reason, the US is infatuated with unusually firm tofu, and supermarkets emphasize the "extra firm" varieties. In Asia, especially Japan and Korea, but even in China, most applications call for a softer, more custard-like tofu.

If it's soft inside, when you deep fry the tofu, it should stay fairly soft inside. The cornstarch or potato starch you coat it with will make the outer bits crispy.