1. The votes can be justified
Questions which have a simple, obvious Yes/No answer are generally disapproved of. See for example the answers to Self Study Students: Confirmation Type Questions and Can we stop closing questions as "unclear what you are asking" for OPs above certain reputation?
The user who provided the only answer to Increasing The Momentum Of A Photon also commented that the question is trivial :
I think it is a trivial question to answer. The OP is simply asking can we increase the momentum without increasing energy. The answer would be simply no. – Dvij Jun 30 at 4:58
What is unclear about this question (in my opinion) is why the asker thinks the answer is more complicated than that. The onus is on the asker to show what his/her difficulty is. Without such context or explanation, his/her difficulty cannot be addressed, it can only be guessed at. In that sense I think the question is unclear even after the edit (v2) and the close votes are justified.
Others may disagree. It is inherent in the nature of reviewing that different reviewers may come to a different conclusion about the same question. Unless there is a policy which specifies what makes a question unclear, the reviewer must apply his/her own individual judgement, rather than try to second-guess others who have not yet voted, or vote with the majority who have already voted. Those who disagree are able to vote to reopen, and have done so.
Clearly you disagree with the votes to close the question as unclear. This is a difference of opinion, not a misuse of the close reason.
The OP has not commented upon nor approved the only answer, so we do not know if this answer has addressed the issue which the OP was asking about.
2. "Not unclear if there is an answer" is not site policy
I agree with @ACuriousMind that the presence of a valid answer does not determine that the question is not unclear. Whether or not a question is unclear (or a duplicate, or too broad, or primarily opinion based, or not mainstream physics, or an engineering question etc) is determined collectively by those who have the rep to review questions, not by those who have the rep to post answers.
Reviewers must be free to exercise their own judgement, independently and impartially, within the guidance provided by site or network policy. If (as it appears to me) you think some policy is being abused, it is up to you make your case by identifying that policy. Otherwise, you are merely expressing an opinion.
If the posting of a valid answer makes unclear what you are asking invalid as a reason for closing, why doesn't it do the same for too broad or homework-like or engineering? Or indeed for all closure reasons? Such a policy would give those who answer the question the ability to over-ride the decisions of those who review the question. It would make the process of reviewing pointless.
The explanatory text for this close reason does not state that the question cannot be answered, but that it is difficult to interpret :
Please clarify your specific problem or add additional details to highlight exactly what you need. As it's currently written, it’s hard to tell exactly what you're asking....
As was the case with the question Reminder that Book Recommendations are on topic, the community continues to close questions contrary to your interpretation of site policy after your "reminder" was posted. For example :
What "things" don't change?
Can you use sun light to heat an objects surface to hotter than the surface of the Sun?
Resistance of filament
Why does the big bang not violate Heisenberg's uncertainty principle?
Is a gravity train really possible? If yes, can it be used as a seemingly endless source of energy?
Are fundamental particles (Electron,Proton & Neutrons) compressible?
Were the reviewers who voted to close these questions abusing the policy "not unclear if there's an answer"? Or is there no such policy?