Yes, there certainly is a difference between 'few' and 'a few', but 'poco' or in this case 'poca' was a new word to us, and in the pull-down menu (that is supposed to teach us the meaning of new words) tells us that there are multiple definitions of this word, and that it could mean both 'few' and 'a few', obviously depending on the context. In their sentence, the context is not obvious, we don't know whether the person is being neutral/or is complaining about not having seen a lot of people. (where 'few' would be appropriate)
On this site you are communicating with other learners, so you won't get a reply from Duo. What you will get is advice and recommendations from other learners. The post by sanio explains the subtle but significant difference between: "few" and "a few". I will give you advice, which you may not like right now, don't sweat the hearts. I have been here over a year, have finished the German tree, doing Italian and Greek now and seldom get through a unit with all hearts intact.
Can you say the sentence "I see few people today." without confusion?
Should it not be one of the following two wordings:
"I see a few people today." maybe if I haven't seen any people for the last week and today there are five or ten.
Or "I see only few people today." if I have seen thousands of people flooding the streets all week and today there are only about a hundred.
"I don't see many people today" -- you are right.
"I don't see many people today" -- right, now it sounds strange to me too. What about "I only see few people today"?
You didn't answer my main question: Does the officially-accepted-English-translation "I see few people today" sound natural to you?
"Vedo poca gente oggi" can be translated either as English simple present tense (I see few people today) or English present progressive tense (I am seeing few people today).
The difference in meaning is much more apparent. "I am seeing a few people today" implies that the number of people you intend to see is a definite number. "I am seeing few people today" implies that you are in a position to see many people but only a few are actually coming to see you.
I think that the reason that the more idiomatic translation "a few" is included is because in some situations it might make more sense. That being said, "una" was not part of the Italian sentence that was translated. For this reason, I myself am loathe to write an English translation that includes the article "a." It's just safer not to push the envelop if hearts are an issue with you.
"Sto vedendo" literally translates to "I am seeing, and "vedo" literally translates to "I see." This being said, it should also be noted that using simple present tense or present progressive tense is frequently a matter of choice because in so many situations the colloquial difference in meaning is negligible in English. Likewise, this may not be true in Italian.