"Jack read a book yesterday" is correct, but not the most natural sentence for this situation.
Simple past describes an action that is finished. It does not mean the action is complete, as in, that Jack read the whole book. It means Jack started reading and stopped reading. Anything that happened in the past and is not still happening now can be described with simple past.
So, in your example, the simple past describes the event of Jack reading the book.
So, what's not natural about the simple past version? In English, when we say that someone "read a book", without any other context, we understand it to mean they read the whole book. It's not a requirement of the grammar, just a convention. If we don't want to suggest that Jack finished the book, then we have several choices:
Jack spent some time reading a book.
Jack read a book for an hour.
Jack read a book until he fell asleep.
Jack did some reading.
And so on.
In English, we tell stories in the simple past. Clauses in past continuous describe things that are not the main story, but background information or context for the story itself.
So in a sentence like "Jack was reading a book when his phone rang" "was reading" always means that reading the book is not the story I'm telling, just a side detail, so if the story you want to tell is Jack reading a book, past continuous is never correct.
As for how this sentence can both mean that Jack read a whole book and Jack didn't necessarily read a whole book, it depends on where you're looking for meaning. The grammar itself just means Jack read something. But if you say "Jack read a book", people will guess that it means a whole book.
It's just convention that things like "I read a book", "I watched a movie", or "I mowed the lawn" usually mean the whole book, the whole movie, and the whole lawn. But it's natural to say, "I mowed the lawn, but didn't finish the part behind the garage". This shows that it doesn't necessarily mean to completion.
If the action is something that can be completed, more often than not, that's what people will infer, but not always. "I watched my favourite TV series last night" does not imply that you watched the whole thing.
And there's no rule about how long something takes, because, "I wrote a TV series last night" does suggest that you wrote the whole thing, even though that clearly takes longer than watching a whole series.