Why? If you translate a sentence then of course, type any correct answer. But if you are supposed to write down what you hear... then you should type exactly what was said. It's how the exercise is designed. Even if we wanted to change it (and we don't), we have no power over this.
Ok, I'm now familiar with the discussion.
Jellei said (paraphrasing) that idzie is equivalent to "he is walking [now]", and chozdi is "he walks [frequently/everyday/etc.]".
"This man is quickly going home" is definitely present continuous (idzie).
"This man quickly goes home" MAY be present continuous in English. It depends on context, and as I said, it would be a perfectly grammatical (and more important, comprehensible) response to "how does this man go home?" or when used in a narrative (e.g. "Bob quickly goes home, then eats a meal.") It CAN also be a description of the general way the man goes, but not necessarily.
Carefully distinguishing between present continuous and present simple has proven itself to be a powerful tool when in comes to teaching Polish verbs of motion. If we didn't do that, we'd be facing a huge problem (we'd need to rework our didactic concept entirely).
Furthermore, without context (we don't assume that this is a narrative) or additional adverbials of time, your proposed sentence will be interpreted as general description by the overwhelming majority of native speakers.
That's what I'm trying to say - as a native speaker, the sentence "the man goes quickly to the house" sounds like a textbook description of what the man is doing (right now), answering the question "how does the man go?" An informal survey of my coworkers asking them to rephrase the sentence had every single one of them choose "the man is going" rather than "the man regularly goes" or any such thing.
But ultimately, it doesn't matter. Duolingo allows "the man eats the apple" or "the man is eating the apple", recognizing that they're both correct. If in this context, you find it useful to distinguish between determinate and indeterminate motion, super. I would just rather than being told it's incorrect Duolingo mark it as "less clear" alternative.
I bow to your judgment and surrender the conversation. Be well.