Earlier quoted context omitted.
I think he means related searches as in http://www.blindfiveyearold.com/wp-content/uploads/2011/06/g... If I understand his comment, if you select the term "sweatshirt" your add is also displayed when people search "American Eagle," and that may be yourself and you're wasting money.
He was referring to running broad match keywords by accident...My point was that its reckless to advertise without understanding match types... Google gives you nearly complete control over which terms they show you on using keyword match types and negative keywords...No one should be advertising with Google without understanding this. https://support.google.com/adwords/answer/2497836?hl=en
It was not clear in your previous comment that "very closely related variant matching" included as well not so closely related variants like synonyms and related searches, given that you said it meant "plural to singular."
> Broad match is the default match type that all your keywords are assigned if you don't specify another match type (exact match, phrase match, or negative match). The Google AdWords system automatically runs your ads on relevant variations of your keywords, including synonyms, singular and plural forms, possible misspellings, stemmings (such as floor and flooring), related searches, and other relevant variations. To help deliver relevant matches, this match type may also take the customer's recent search activities into account.(https://support.google.com/adwords/answer/2497828)
Edit: The critique above may not be fair because your point seems to be that "broad match" is not the default setting (so you really think that the default shows only very closely related variants and not synonyms or related searches). However, if this is what you really meant then you seem to be wrong.