The "cue" she picked up on was Andrea telling her that her child has wonderful parents. Plural. She as complimenting them both. In the wife's mind though, that became a compliment directed solely at OP and an indication of sexual interest. It sounds to me like she's jealous and her mind is working overtime. If he gets rid of Andrea for no reason, I wouldn't be surprised if the wife said no female assistants at all.

Also, it is not abnormal for a company to send its employees back to school for further training. They decide to invest in their employee's future, banking on that employee feeling invested in the company as a result, and both growing side by side.

I think you're making up that this post is "defensive", and I think you're looking for stereotypes. You assumed he was traveling alone with this woman; not sure why. Then you assumed the MBA was odd, when it's not. It's not at all baffling to understand why the wife would be going wild with speculation - you just did, too! See how easy it is?