I don't understand what is so terrible about what Trump said, unless you are falling into the media error of parsing everything he says literally.
He is saying he took over a country with a terrible debt problem, one that the media were totally silent on as Obama ran up more debt than all other presidents combined. Despite this obvious problem, the stock market showed such faith in Trump that it rose by $5 trillion. Obviously the two do not directly offset, but viewed from the perspective of the national balance sheet, an extra five trillion on the asset side is nothing to sneeze at. Some of those gains will be reflected in cap gains tax revenues and the wealth effect causes people to spend more, adding to GDP.
They don't even indirectly offset. The statement was so stupid that it was for the record books.
As for the stock market specifically, it has absolutely nothing to do with Trump. If it was all about the Trump tax plan, then it would have dropped when that tax plan was not likely to pass, or when it was identified to be as poor a program as was leaked.
Additionally, let us not forget how Trump ran his campaign with the comments about the Fed propping up "one big fat ugly bubble" for Obama. And now the market is much higher...but he cheers it.
The guy is a tool.