TLO is to Starcraft* as Fan Hui is to Go. They are strong players but not the best. I am guessing that Deepmind knows that the strength of their bot isn't ready to take on the very top players, and wanted to show off against a well-known personality in the Starcraft II scene.
Incidentally, though, the strongest Starcraft II player currently is arguably Serral [1], who is Finnish. He beat the strongest Korean players to win the WCS World Championship last year.
[1] https://liquipedia.net/starcraft2/Serral
* at least TLO's skill level when offracing as Protoss. His main race, Zerg, is very strong, ranked around 70-80th in the world.