The Christian re-interpretation of ‘son of man’ is a corruption (which itself was likely present in various sects of Judaism in the first century) of the original intent, and the original word in Daniel 7:13 just means ‘a human’. Compare similar usage of ‘son of man’ throughout Ezekiel. As used in Daniel, it conveys (hyperbolically) that a new king in the line of David was expected to arise. The corruption of the term likely developed after expectations failed regarding the appearance of a human messiah in the years after Daniel was written in the 2nd century BCE.
See also Ezekiel revisited - Teaching Box 7B (review of Pure Worship book).