It refers to the one who withholds in spending in good and charity to the poor, orphans and the nearby.

وَاسْتَغْنَى (considers himself free of need): Considers himself free of need for what with Allah (swt), he dispenses with the paradise’s pleasures for life’s enjoyments.

The withholding here does not just concerns the giving, rather, it is the withholding of Allah (swt) and His rewards.