> Because lists are dynamically typed and heterogeneous, does that mean the underlying C is basically a contiguous segment of memory of python object references?

Yep, it is an array of pointers: https://github.com/python/cpython/blob/3.7/Include/listobjec...

> And when the list needs to be resized and doubles itself, it's just doubling the space for object references?

Basically yes. The growth pattern is not as aggressive as doubling though: https://github.com/python/cpython/blob/3.7/Objects/listobjec...