@Justpickitup I applaud you for following your instincts and wanting to keep your family safe I would do the same if I felt a niggle too. I can see why you are nervous because it can be misinterpreted.
But if my partner told me after the event that they had checked me out in this manner, I would be gutted. I would imagine that the rational, intellectual side of his brain would say that he has done nothing wrong so has nothing to hide and she is protecting her children which shows she is a great mum. Indeed if you were his female friend and told me the scenario, he would likely say do this to set your mind at rest.
However if I were him, the emotional side of me would be questioning what it was about me that set the alarm bells ringing and what I did to raise this concern in you. It implies an element of distrust. Intellectually, I would accept it, emotionally I would struggle with it. Keep it to yourself.
You absolutely did the right thing, just don't discuss it with anyone. Keep it, file it and know your kids come first when bringing a new partner in your life. This facility is not to be used lightly, as a standard boyfriend vetting process, but when the itch comes, scratch it and follow your instinct.