That's not how it's recounted in the Isaacson biography. Jobs says it was pitched as "Think Different." and that they debated Different vs Differently after it was pitched.
This chokes me up, this really chokes me up. It was so clear that Lee loved Apple so much. Here was the best guy in advertising. And he hadn’t pitched in ten years. Yet here he was, and he was pitching his heart out, because he loved Apple as much as we did. He and his team had come up with this brilliant idea, “Think Different.” And it was ten times better than anything the other agencies showed. It choked me up, and it still makes me cry to think about it, both the fact that Lee cared so much and also how brilliant his “Think Different” idea was. Every once in a while, I find myself in the presence of purity—purity of spirit and love—and I always cry. It always just reaches in and grabs me. That was one of those moments. There was a purity about that I will never forget. I cried in my office as he was showing me the idea, and I still cry when I think about it.
They debated the grammatical issue: If “different” was supposed to modify the verb “think,” it should be an adverb, as in “think differently.” But Jobs insisted that he wanted “different” to be used as a noun, as in “think victory” or “think beauty.” Also, it echoed colloquial use, as in “think big.” Jobs later explained, “We discussed whether it was correct before we ran it. It’s grammatical, if you think about what we’re trying to say. It’s not think the same, it’s think different. Think a little different, think a lot different, think different. ‘Think differently’ wouldn’t hit the meaning for me.”