Very true, and you're right that these are totally different forms of validation. It's a steep learning curve (for me), but I figured this particular blind spot may be encountered by some (definitely not all) other tech folks on this path.
Without reaching out to my customer first, my MVP wouldn't have solved their needs as effectively -- and there would have been too many holes in critical use cases.
After watching all the Steve Blank videos on Youtube, I'm a believer in "get out of the building and talk to customers".