Ann: Investment from Lithium Americas Corp and A$55m Equity Raise, page-21

The 8 Nov 2021 "top 20" shareholder list was actually the top 43 because it counted the top 20 discrete shareholding values (so the 11 shareholders with exactly 1m shares were spot 19). At listing the top 40 were all 1,000,000 or larger. Any one of them would be able to generate a sale this size.

The sale may well be related to the capital raise. With T+2 settlement its its possible to sell shares on Friday and use the sale proceeds to pay for shares acquired in the capital raise. Payment isn't required until Wednesday next week. If they also had tax losses were available, triggering a capital gain from the sale wouldn't be an issue.