It's easy to forget why we use the simple and continuous tenses, but after a quick review the answer to your question is quite easy.
We use the simple form to state (amongst others) truths, facts, that an event that took place and so on.
We use the continuous form to focus on the activity taking place (amongst others).
You also have stylistic reasons for using the simple and continuous. I encourage writers to use to use the continuous to give the idea to a client that something is being done, or to communicate a sense of urgency.
You might you the simple form to build tension, set context and so on.
In the examples you gave, without further context, i'd say the simple is being used to set a context for what happens next or to build drama in the present context e.g. I told him I was leaving him. He sat there and crunched his cornflakes.
To get the best translation, you really have to get to the heart of the context - particularly if the tense is being used stylistically.