It's a standard reason for declining a flag - and I was the person who did that. However, I wouldn't take it as a personal rebuke to have a flag declined in this way.
I agree it's not a great question, but it's not 'low quality' which would mean that its barely legible. From the description when you choose a flag type:
This question has severe formatting or content problems. This question is unlikely to be salvageable through editing, and might need to be removed.
By flagging it you are essentially asking for someone to intervene, in this case either:
Someone to delete it. I don't think that's the right way to encourage people to contribute more to the site, by some arbitrary quality standard that will vary from day to day, depending who reviews the flags.
Asking someone else to step in and improve the question. Everyone should feel empowered to edit and improve content here - this isn't just the role of the moderators. You yourself could do this.
The question doesn't in my option meet the standard required for removal as outlined above, and doesn't meet any other reason for removal, such as being off-topic, or contain spam or abusive material. Therefore I was obliged to decline the flag.
As a side note, this related meta question asks about low-quality Answers, but the content there is relevant to this discussion too.