In most brokerages, you can execute even OTM options. With SP under 150, one could contact the firm, execute the put and buy the shares in the same trade.They can exercise it later for sure but I think the final SP is the closing price so -P150 should be safe but it's all in the exchange contract. The fairest price is when there's more trading volume (i.e. normal trading hours).
However, the drop below 150 was minimal so no great incentive to do so.