buyer and seller must be known to each other, and they have...

buyer and seller must be known to each other, and they have organised to do this trading today. Normally this sort of exchange would happen as an off market transaction. Very unusual to do it on market in this way.

If someone was dumping this many shares without a buyer having been organised, the price would have completely collapsed. Very unusual trade sizes, not even quantities.

Notice the 1mil order at 15.5c to prevent the price from falling if other holders start dumping their holdings.