I can quite believe this average. I have a 2006 GLi, and after reading the hypermiling techniques by a member of PW with a Honda City, I implemented them on my car. My car has CNG kit installed and I have tested the hypermiling technique on CNG only. Previously within city my GLi used to give me 120 - 125 km in one gas tank of 55kg. For the last two tanks (driven using hypermiling techniques) I have managed to achieve 176 km first time, and 184 km second time. So Altis at 17.6 kmpl with hypermiling techniques? Very very believable.
Btw, the PW member who posted the hypermiling techniques thread has 2010 City and his car gives an average of 26 kmpl.