Whether it meets code or not is not the question you should pose. It�s your project and if you�re not satisfied with the side walk have the contractor replace that section. When concrete sections are replaced the new section should be tied into the old section with rebar and made level with the old section. If its not tied in there is a good chance that over time the two sections will move in relation to one another.

sidewalks are not necessarily tied for thier fiull length, that is why one sees so many sidewalks with discontinuities due to roots underneath or differential settlements. Additionally, sidewalks that are "tied" often do not have the strength to bridge over the differential settlement and will spall at the reinforcing as it tears out laterally.

Depending on the thickness of the section and the distance between joints, the contractor may be able to eoither jack up the settled side or lift it enough to put more back fill under it to even it off.

New sidewalk, it should be at the same level as the old sidewalk. As you mentioned the difference is a tripping hazard that you would be liable for.

Call them back and get it fixed.

If this section of sidewalk abuts the lowest step riser, raising it may affect the required consistency of riser height.
As I recall, there can be no more than a 1/4" variable, tred to tred.