It's not a typo, it's just unecessarily confusing. The connection goes localhost:55432->dataserver:5555->dataserver:5432. 5555 and 55432 are arbitrary numbers (5555 came from a web page I was getting an example from, 55432 is the first slight variation on 5432 that came to mind). It would probably be better to pick different numbers to avoid just this kind of confusion.
