These are the players they've signed, according to Transfermarkt.
The players they've signed from Europe this summer are:
Alex Telles, Birama Toure, Alin Tosca, Seko Fofana, Andrei Burca, Virgil Misidjan, Bernard Mensah, Gojko Cimirot, Sergej Milinkovic-Savic, Flavio, Roberto Firmino, Jota, Marcelo Brozovic, Edouard Mendy, Kalidou Koulibaly, Ruben Neves, Ngolo Kante, Ivo Rodrigues, Karim Benzema, and Pedro Rebocho.
That's 20 players. Most of them are not recognizable. A few aren't even coming from 1st division clubs. Hence "a little over a dozen players."