He did get roasted, and it didn't help, but don't kid yourself that it was the catalyst, he flipped a couple years before that happened. I read that same story, and it was just an fluff piece for the media.

https://www.sbs.com.au/news/article/donald-trump-was-once-a-registered-democrat-and-party-donor-why-did-he-jump-ship/wj85mj5yq

He's changed affiliations 5 times now

Before he ran, his investments were petering out. He owed a substantial amount of money to multiple places. (notably a couple of billion to Deutsche Bank) His contributions to whatever party he was sucking up to were in the couple of thousand-dollar range.

He registered Republican near the end of Reagan's run. He flipped to Independent in the middle of Clinton's presidency. He switched to the Democrats when Bush took office. He flipped to republican the year Obama got in, even though the roast was two years before the roast in question.

The Republicans knew that once Obama got in, they could weaponize race and he turned out to be the face they were looking for to empower the right extremists and moderates.