Absolutely! I have never ever heard someone say 'Heb je nog enkele vraagjes?'. The only time I would consider saying this is when a friend is testing me on my ability of translating small questions and I want to know whether he has a couple more questions or all the questions are translated. However, I don't know what Duo thinks about this.
I think it might just be here to demonstrate how EVERY noun has a diminuitive form. That form is gramatically correct but its usage may vary on context or it might just not be commonly used.
Like, "Frägchen" in German technically exists, as it is constructed correctly. You don't hear it on the streets, though, or anywhere else really. Still, if I was to decidedly, maybe comically, beat around the bush about something I might actually say "Also, ich hätte da noch so ein paar Frägchen ...", making my utterance very evasive and soft.
That said, I don't think Duolingo is made to teach me practical, everyday sentences that I can throw at locals to get what I want. I'm here to learn how to use a language, and that includes its word building capacities. If I use "vraagjes" in the Netherlands and get weird looks I know not to do that anymore - but I am still able to do it when I want.
It's not that simple:
"We use the weak form of some in affirmative sentences and in questions (usually expecting the answer ‘yes’), when the quantity is indefinite or not important (we use any in questions and negative sentences)"
In other words, both can be used for questions.
While it is true that some can be used in questions, note that using some implies that you know/expect that your interlocutor will answer 'yes'.
Using any turns the question into a 'real yes/no question', that is: you don't know whether your interlocutor will answer yes or no, you don't expect any of the two in particular.
So there's a difference. Of course, we don't have any further context here, so we cannot be certain which one should be used, it's open to interpretation.
But keep in mind that when one elides the 'do you still have'/'have you still got...' part, the resulting question (very frequent in lectures and conferences) becomes Any questions?