My max bid was the same as the winning bid (tie bid), yet someone else won it. Why?

In the case of a tie bid, the hammer will always fall to the first bidder. For example, the current bid is $50 (placed by someone else). What you don't know is that their max bid (which is masked from other bidders) is $200. You join the bidding and and place a maximum bid of $200 and are immediately outbid in favor of the other bidder. Even though two people have the same max bid, only one person can win the lot. That is automatically determined by bidding order -- the person who placed that maximum bid first.