Cape Town is 18.5E, 15E is far out in the Atlantic Ocean, and flying SW goes even further offshore (nowhere near Table Mt). The lack of airports matching that location in the database would be more likely to trigger a warning (with gear down).
A rather similar navigation error (insufficient decimal digits) in Brazil in 1989 led to a much less happy outcome:
https://en.wikipedia.org/wiki/Varig_Flight_254