Both DT and UCD is about putting your self in the shoes of the user.
I would say the main difference is that Design Thinking is a method to develop solutions which nail the actual problem which the user has, which are not mainly User Interface related.
It can be service design orientated, or to come up with a new product idea, etc. I would even take the bold move to say that DT is mainly about Ideation.
Whereas UCD focus area is HCI (human computer interaction). It has indeed the same process steps. But UCD is way more restrained in terms of "when to use which method or tool" since it is clearly focused on User Interfaces.
Other than that, the toolset which Design Thinking brings to the table is extremely valuable for the discovery/research phase in UCD.
In my career as an UX specialist I've been often asked to explain the Design Thinking methodology. It is heavily related to each other, but UX has it's clear focus on User Interfaces. Well at least if you want to make this clear definition of what UX is ;) I'm not a friend of this "UX is everything" talk, this doesn't help anyone understanding UX ;)