If you read that first link it will explain because of this short volume, all trades are marked short or long, but it is complicated, when you sell shares, there can actually two separate transactions, one short and one long. ( Sometimes both will show up on the tape on otc, but they are not suppose to). Also daytrading creates shares sold that hasn’t been received yet, which will be label as short and enough of this can set off regsho. A daytrader sells shares to another they bought same day, well that is going to take 6 days to sort out, and will be labeled short volume. Also some market makers, like cdel, have their own trading side, which can go short if they see weakness in bids and cover same day. So heavy short volume does not always mean heavy shorting. Of course heavy shorting would show heavy short volume, so it does work one way, but not always the other.