That is largely if not entirely true.

His reason for not showing it until now is probably as you say, contrary to the narrative he was advancing of being a prodigal business man of un-encompassed measure.

Except he isn't, and after in essence, gross incompetence and mismanagement of his Casino's in Atlantic City, incurring estimated 916 million in losses, most of which was not even his own money, he was able to get a tax deduction equivalent in amount of taxable income over an 18 year period as the NYTimes article points out. His loss then become a tax avoidance strategy; and it was legal.

His campaign then claimed, “Mr. Trump knows the tax code far better than anyone who has ever run for President and he is the only one that knows how to fix it.” And the talking point memo religiously repeated by all his surrogates was what a brilliant acumen for matters concerning taxes does our Lord and Saviour Trump have.

Except he had no hand whatsoever in filing his taxes, as he former accountant who actually did the taxes stated in a CNN interview. He also added that Donald Trump had a "brash and undisciplined style, lacking sophistication".

https://www.youtube.com/watch?v=uvurx8jyOmY

The man is a total and utter fraud. His whole brand is selling 'rich' to those gullible (or susceptible) to buying it.