I reviewed the flag, and this was my thought process:
Is this question actually off-topic? I determined that no, in my opinion, it was not off-topic. Business concerns1 are listed as something that is acceptable to ask about. Interviewing techniques are absolutely a business concern. In addition, I have participated in screens and interviews as an engineer, as have my colleagues. Since it was about a technical interview, and not general interviewing, I decided that it would best be answered by technical people.
Is it constructive? Absolutely. There's not a narrow scope of answers, but I believe that there might be some common threads across answers as to what constitutes a "9" or a "10" for a Java developer, and some expert Java developers or those who frequently interview Java developers would know what ideas of topics should be included. Of course, one of the things that I would have asked in a clarifying question would be more about the toolchains and environments used, the external libraries used, the domain of the system, what kinds of applications were being built, and so on.
Is it a question that makes sense? From the perspective of a technical interviewer, yes, it does. First, in interviewing, there is the concept of illusory superiority that any interviewer must deal with. Asking an individual to rate themselves and then basing the interview on that is a valid technique. In addition, the most proficient Java developers and those who have hired other Java developers would be able to share their expertise as to what makes a "1", a "5", and a "10" and so on.
Who flagged the question? I saw that the community was expressing their opinion on the question through votes to close and downvotes. I also saw that the flagger had voted to close the question. I felt that it was inappropriate to flag a moderator for a new, still active, question that the community was dealing with. There was still opportunities to enhance the question, ask for more detail, or provide feedback as to how to make it better. I'm not going to step on the community when the community is handling it just fine.
Was it a perfect question? Absolutely not. If I had more time when I was reviewing flags, I would have edited the question or asked clarifying questions in comments. If it was a low reputation user flagging, I would have dismissed it as helpful, but taken no action to let the community respond through voting (up/down and closure). I just saw no need to support the community's efforts to police themselves and was not about to step in with a binding vote for a moderator. If things were slow or it was a question that I was sure couldn't be salvaged, I'd have stepped in, but that was not the case in this instance.
1: Business concerns is vague. My rule of thumb to determine if a business question should remain open is two fold. First, is it something that would be discussed in a business course or known by people with a background in some kind of business (management, finances, accounting, human resources, etc). Second, is the education and experiences of a software development professional pertinent to the question. If both are yes, it's on-topic.