Exegesis:

idōn ethaumasen hoti ou prōton ebaptisthē pro tou aristou lit. ‘seeing he wondered that he did not wash before the meal’ Though syntactically the clause introduced by hoti depends on ethaumasen only, it goes semantically with idōn in the first place. prōton … pro tou aristou lit. ‘first … before the meal’ (cf. Revised Standard Version), but many translations do not render prōton specifically.

baptizō lit. ‘to dip,’ here ‘to wash,’ the hands presumably, cf. Mt. 15.2.

ariston (also 14.12) ‘breakfast,’ ‘noon meal,’ ‘meal.’

Translation:

Was astonished to see, or, “was surprised when he noticed” (Good News Translation). For astonished cf. “wondered” in 1.21.

Wash. In some languages an object has to be added, ‘wash hands’ (Bahasa Indonesia), in others a derivational form of ‘to wash’ has the meaning ‘to wash one’s-hands-or-feet’ (Sundanese), ‘to wash-one’s-hands’ (Batak Toba). That the verb has a ritual connotation here is sometimes made explicit, cf. faire des ablutions (Bible de Jérusalem, similarly Zarma).

Quoted with permission from Reiling, J. and Swellengrebel, J.L. A Handbook on the Gospel of Luke. (UBS Handbook Series). New York: UBS, 1971. For this and other handbooks for translators see here . Make sure to also consult the Handbook on the Gospel of Mark for parallel or similar verses.