"No estuvimos durmiendo el viernes."
Translation:We were not sleeping on Friday.
Is this really a correct usage of the past progressive? Doesn't it need to be imperfect? Estábamos durmiendo?
I think it's OK. A lot of the sentences DL has come up with in this section sound weird because they are variations of the typical English, ie in this case: "We did not sleep on Friday." By injecting a gerund into the sentence DL creates a structure that sounds unnatural, but is technically OK. However, as Howcheng points out, the form of the resulting sentence does leave you with a sense that it is suggesting "we were not sleeping [because we were up to something else]."