I'm sure you can elaborate. "Yes, my instrument and CFI. I learned more from those experiences than all of the checkrides I have passed combined."
You might get a follow up giving you an opportunity for a positive response, or it might move on. "I didn't realize what I didn't know, I studied it and it may have saved someone's life when XYZ happened 2 years later." I am nearly certain all of us could give an honest answer similar to that regarding a checkride bust.
Interviews are an opportunity to paint yourself in the best light. The circumstances and questions don't matter -- you are already talking, that's the hard part. Getting there. The answers are what you control. Think about the message and impression you want to leave, and work backwards from there.
Elboration is fine, but most people are fairly unskilled with speaking about a perceived negative. If it takes more than a couple minutes, max, to describe the failed upgrade (compared to ten-plus minutes), you're doing it wrong!

