We could also group this with the fact that he is a perfect reader of his environment. Since when he takes a first look at the family, he notices that they are nervous, he even sees one of the daughters looking at the ground while looking at her father, an undoubted act of nerves. Landa with the excuse of greeting her for looking like the most Aryan in the family (The Aryan race was the one preferred by the Nazis), using this as an excuse to grab her hand and kiss her, at the same time he tends to check the young woman's pulse.