The inspector should become knowledgeable about detecting and analyzing settlement problems and cracks.
All buildings settle to some extent usually within the first year or two.
This is typical and should be reported as such. It should be mentioned in the report though and stated that the settlement appears to have stabilized. The inspector can't call for expert every time a defect is noted, or the client will question the need for an inspector. The analysis is based upon the experience and judgement of the inspector. Be that as it may, when judging structural cracks, consider the size and freshness, as well as the type of crack.