Yes, self-funding was a definitely the core part of the plan. Here's the original "master plan" text from 2006 [1]

  Build sports car
  Use that money to build an affordable car
  Use *that* money to build an even more affordable car
  While doing above, also provide zero emission electric power generation options
  Don't tell anyone.

I think the term "that money" ('that' is italicized in the original) is pretty clear he means funding from the profits of the prior models. (Elon Musk has definitely articulated the funding thing in interviews.)

Also, the summary Elon Musk has just posted continues using the same italicized emphasis:

  Create a low volume car, which would necessarily be expensive
  Use that money to develop a medium volume car at a lower price
  Use *that* money to create an affordable, high volume car

[1] https://www.tesla.com/blog/secret-tesla-motors-master-plan-j...