Seems pretty simple.....Have you been a part 141 instructor? Either you have or haven't.
The instructions are general because the questions are specific. If you mark yes and then explain that you once had part 141 instruction, The response will most likely be RTFQ! Not trying to be gruff but I would just answer the questions as written.
Have you been a part 141 instructor? yes/no
If it is yes then elaborate. If no, then no explanation required.