once upgrade completed we also need to clicked on finalize button to complete the upgrade process. if you have done this and still see previous version of spark then you should login to node and manually check spark package version through "rpm -qa|grep spark" command.
Agreed, you should at least upgrade the lower HDP version (...2.3.0...) to the newer HDP version (184.108.40.206-3485). It is best to get the default Spark version from the HDP install. Please see Table 1.1 at this link which describes the version associations for HDP, Ambari, and Spark: