I would hesitate accepting it. "До скорого" is indeed "see you soon", but it is even more informal than "see you soon" in English. That is, I cannot imagine saying it to anybody whom I would address using "Вы" instead of "ты". On the other hand "Goodbye" and even "see you soon" are quite neutral: I can say "See you soon" to my doctor after making an appointment (assuming the appointment is sufficiently soon). I would never use "До скорого" in Russian in such a situation. Since learners will likely not have a feel for such niceties, I think Duo is correct teaching neutral expressions instead.
До свидания literally means something in the lines of "until the date". It's a idiomatic expression, so this date is the the time people will get to see each other. If you mean to say goodbye, or godspeed, meaning that you either don't plan or don't know if you will meet someone in the future, simply say прощай.