An answer should be deleted when it does not answer the question.
A partial answer is not a valid reason for a Not An Answer flag, so partial answers are answers, and so should not (generally) attract delete votes.
Leaving a partial answer, and a comment for further clarification, was a correct approach here (not the only one). Leaving the partial answer as a comment would not have been correct (or helpful).
All that said, we don't want a site full of borderline questions with large numbers of borderline answers. A general rule is to close early and often where appropriate, as this helps people to learn what is needed for a good question, and raises overall quality. So, another 'correct' approach would have been not to answer, and vote to place the question on hold pending improvement so a fuller answer could be provided.
Clearly, your considered judgement was that the question was answerable enough that a partial answer was the right thing to do, and I respect that decision. For clarity, it would not have been fair to answer and also vote to close (which you did not do), as this would prevent other people answering as you did.
As to how this all came about, your initial answer was flagged by the system as low quality (algorithm not disclosed). This started a Low Quality Post Review, where the reviewers pretty much have to make a binary decision between recommending (voting) to delete, and leaving it be.
My advice: Think carefully in these types of situations whether it would be better for everyone if the question were placed on hold instead. If you choose to leave a partial answer after making that careful assessment, make it the best partial answer you can.