At the top of the page right side is the help link, click it, 1/4 of the way down explains how it’s determined to categorize the transaction as a buy or sell. Looooosely I think of it did the transaction occur at the bid=sell or ask=buy?
The 'Buy', 'Sell' and '?' columns - Where the 'Price' is closest to the 'Offer' price, the trade is considered a 'Buy'. Where it is closest to the 'Bid' price, the trade is considered to be a 'Sell'. Where it is dead centre between 'Bid' and 'Offer', it appears in the '?' column; this indicates that the trade cannot be identified as either a 'Buy' or a 'Sell'.
The 'Buy %' column is a graphical representation of the ratio of Buy : Sell : ?
The 'T.Buy', 'T.Sell' and 'T.?' columns represent a daily running total of quantities for each type of trade.