It's certainly legal, but it often feels uncomfortable to me. The NALC model standing orders, which many parish councils use, includes the following paragraphs on the matter:-
3(e) Members of the public may make representations, answer questions and give evidence at a meeting which they are entitled to attend in respect of the business on the agenda.
3(f) The period of time designated for public participation at a meeting in accordance with standing order 3(e) shall not exceed ten minutes unless directed by the chairman of the meeting.
3(g) Subject to standing order 3(f), a member of the public shall not speak for more than five minutes.
3(h) In accordance with standing order 3(e), a question shall not require a response at the meeting nor start a debate on the question. The chairman of the meeting may direct that a written or oral response be given.
There may, of course, be good reason not to respond. It is possible that nobody knows the answer to the question. Further research may be required. There may be no simple answer and insufficient time to enter into a lengthy debate on the matter. The Transparency Code requires councils to provide at least three clear days notice of matters to be discussed at a meeting, so for many issues, the correct protocol would be to add the item to the next agenda.
Having said all of that, in my experience, the matters raised may be relatively straightforward in nature and capable of being answered by the Chairman or Clerk, either at the meeting or by e-mail the following day, thereby fostering positive relationships between the council and members of the community.
Incidentally, I presume that the minutes of their previous meeting included a reference to the decision and explained why the decision had been made?