The interviewer can see that you have previous positions which qualify you for this job with ECM, Inc.; however, they want for you to go into further detail on the roles which you feel are the most relevant to the position at hand. This question also helps the interviewer to see that you understand the job description and requirements of the role. If you do not understand the position requirements fully, a question like this will make that transparent to the interviewer. Be sure you know your stuff! Use the keywords provided in the job posting/job description to keep the attention of the interviewer.
"From my understanding of this position, you are looking for a professional who is skilled in X, Y, and Z. I bring about seven years of experience in each of those skills - primarily from my jobs with Company A and Company B. In total; I have over ten years of industry experience which means a full understanding of your organizations' primary focus."
"I feel that my current position is the most relevant to this particular role with ECM, Inc. because we use the same software, and the business model is very similar. My current position aside, I have approximately ten years of related experience in skills A, B, and C - which you mentioned as required skills for this position."