He will need a good CPA to declare which assets were long term investments and which fall under mark-to-market day trading rules, but he won't need to pay $800k.
tl;dr: clickbait (mostly), but do read up on the wash-sale rule if you intend on day trading in order to save yourself an end of year headache.
https://www.irs.gov/taxtopics/tc429
He will need a good CPA to declare which assets were long term investments and which fall under mark-to-market day trading rules, but he won't need to pay $800k.
tl;dr: clickbait (mostly), but do read up on the wash-sale rule if you intend on day trading in order to save yourself an end of year headache.