It means that the top player on the leaderboard has the highest number of babies born in their village. To have your score appear on the leaderboard, you must have had more babies born in your game than the number listed for the person in 50th position.

The leaderboard actually says "Tech Points" rather than "Tech hours." That is simply referring to the number of "Points earned" recorded in the game's statistics screen (where all of the other stats on the leaderboard page come from, as well).

The music is original music composed for Virtual Villagers, by the way.