That would be weird, but "he's not a great investor" is taken out of context from "he's not a great investor in the way people think". The way it would be said is "he's not a great investor in the way people think [stock picking], he's a great investor because he found this other strategy that works well."

What about he's "not a great investor in the way people think" leads you to believe "he's not a great investor"?