This "William L. Black" (possibly known as "Larry") was at that time an undergraduate at the Massachusetts Institute of Technology, investigating Hex and Bridg-It, two games based on the challenge to create a connected "chain" of counters that link opposite sides of a game board.
The player who first causes the path to run back into the edge of the board loses the game.
[1] As outlined in the example games provided, the player who routes the path into a corner of the board will win the game, as the other player will have no choice but to run the path into the edge of the board.
This strategy was discovered by Black's friend Elwyn R. Berlekamp,[2] who subsequently described it in his book.
[1] For a rectangular board with an odd total number of squares, i.e., when both sides of the board are odd, the second player can instead win by using a similar domino tiling strategy occupying every square except the one containing the first player's first move.
If Player 1 makes the move [B4]-T3 that will result in an instant loss, since this tile will link the path to the bottom edge.