This actually depends on whether the ear atresia is an isolated congenital anomaly or associated with other congenital anomalies (ocular-facial-vertebral-cardiac-renal...etc) as a syndromic condition. The likelihood of recurrence in the subsequent siblings is rare in the first possibility, whears it depends on the identified syndrome in the second one.

The ear atresia in this child is less likely, but not absolutely, to have a genetic basis,  If a thorough medical examination and meticulous investigations revealed no other congenital anomalies together with the negative family history.

I am by no means an expert on this disorder but the experts above have provided you some answers. After some research on the subject, it appears atresia is congenital, which means present at birth, but not necessarily genetic.   There are other ear developmental disorders such as microtia, which can have a genetic basis, such as syndromic chromosomal disorders such as 22q or charge syndrome.  What makes it more complicated is that atresia and microtia can occur together, which might lead one to think atresia genetic when it is from the microtia.  As Dr Abdelkreem stated above this confusion can arise from multiple syndromic or congenital birth defects in the same individual.