It boils down to a semantic argument. People have differing definitions of what it means to "think about committing suicide". If you're up on top of a tall object and happen to imagine yourself plummeting over the edge even without any intention to do so, some people will consider that "thinking about it", and some people won't.

The useful interpretation is to exercise empathy and put yourself in the mind of the person writing the questionnaire, and ask what definition they are likely using. For example, your therapist doesn't care if you had a random intrusive thought thirty years ago, they care if you presently have actual designs of self-harm. Likewise, in the OP, the person interpreting the security clearance doesn't care if you were accidentally caught up in a silly witch hunt when you were 12.