Translation:That night Andrea was drinking beer and I was eating a sandwich.
Hi rspreng! I know your post here was a year ago but you're posts/explanations are always so helpful to me. I was hoping you had a suggestion on where I could go to get a handle on all these verb tenses and how they translate between English and Spanish uses. They don't always seem to correspond to one another.
That's more of a guideline about what kind of idea someone saying "that night" is probably going to express - talking about an event that happened at a specific time, which would use the preterite
Take a step back for a second
that night I was eating a sandwich
that night I ate a sandwich
these have subtly different meanings, right? A different sense you're trying to get across, the first one can be used for setting the scene before you say "then this happened", that kind of thing. The second one is more common (hence the advice in your notes), but they're both valid ideas you might want to get across, and you use either the imperfect or preterite to express one or the other. In this case, it's the former "at this time this thing was happening" being expressed, so it has to be the imperfect
I don't think that's quite right, regardless of any computer understanding. When you form the progressive "was drinking" you use estar and not ser. The verb ser is more often used for forming passive voice expressions (when part of a verb phrase). La cerveza fue bebida por Andrea - "The beer was drunk by Andrea."
If you did say/write estuvo bebiendo rather than bebía, you would be making a point about the time during the drinking. It's like saying "while she was drinking" this happened. The sense of "was drinking" communicated by bebía doesn't draw special attention to the while-it-was-happening aspect. It's merely a distinction between the idea that "she drank" vs. "she was drinking." You aren't trying to say anything about what happened while she was drinking. Using the imperfect merely lets the action be open ended.
So, it's sort of:
Andrea bebió - she drank
Andrea bebía - she was drinking
Andrea estuvo bebiendo - (this happened when) she was drinking
Hopefully, that makes sense. The problem for us gringos is that we don't make all these distinctions via changes in verb tense and aspect, etc. We just use a lot more words and context to communicate the differences.