Could be a trader or algorithm testing the market without...

Could be a trader or algorithm testing the market without committing, could be a portfolio rebalance, could be a trader looking behind the curtain to see liquidity or any number of other reasons. It is not at all uncommon during trading hours.

The daily auction begins at 4:00 pm and typically runs for 10 minutes. It is often conducted alphabetically but not always, so that particular trade at 4:10:33 pm could have either been inside or outside the auction trading time. The trade may have been made to test for market sentiment, it could also be used to influence the closing price (particularly in stocks which are very thinly traded), or also could have been used to establish a position before an event which is likely to influence the SP in the next day's trading session.

There's a host of other reasons such as fractional investing, capturing dividends and other suchlike things which are not likely to be applicable to this company.