This is correct--EIGRP auto-summarization only takes place when there are two interfaces (or connected routes) on the same router, both 'covered' by EIGRP network statements, in different major networks. Redistributing an interface in one major net into EIGRP, and running EIGRP on a different interface in a different major net, on the same router, will not cause auto-summarization to occur.
This is covered, I think, in the eigrp white paper on cisco online, which is currently being revised.
Russ