Spanish speakers often give only a slight emphasis to a final S. I wish they wouldn't, but it's their language, and that's what they do. So it would be normal to hear something like abre instead of abres.
You are right that abre is the imperative (command, maybe even a demand), but the pronoun would normally not be included. Duo's original is not a command.
This discussion is about the Spanish source sentence. What were you asked to do in this exercise? Write in English? Type what you hear? Complete the sentence?
"You open the door" would normally not be considered to be in the imperative, because a subject is present. Do you mean "You, open the door"? That is different. But we are supposed to be working with the Spanish sentence here...
In another lesson, we were told that apparently 'neutral' questions like "¿Me traes un vaso de agua?", "¿Tú abres la ventana?", etc are actually requests; hence, being included in the "Requests" lesson, I wonder if all these apparent statements (Tú abres la puerta, Tu lees muchas paginas,...) are actually requests as well. Can you use a statement as a command in Spanish? and, if so, would this be a 'normal' request, a hidden, polite request or rather a rude one? (In German, this would be a very bossy, no-kidding way to request that someone opens the window.)
It sounds odd to me to say "You open the door."-- don't they know what they are doing? The same with "you are opening the door." When would you use such a sentence? Is it a request, an order, oh, you actually can do that? (The baby did it), you pushed it open accidentally and didn't notice???? Is there another way it would be said?