When Cognos 10.1.1 was released, it introduced a new Java based query engine called Dynamic Query (DQM).
The previous query technology was C++ based and thereafter referred to a Compatible Query in the documentation (CQM).
Connections to data sources from CQM require the appropriate 3rd party database client libraries (i.e ORACLE OCI, Informix-Connect, Db2 Data Server client) to be present on the path used by the operating system to load dynamic libraries. Should you attempt to use a connection (test, run report) etc, the machines where that activity occurs must have those database clients installed/configured. Not doing so will result in errors from the operating system re being unable locate libraries etc.
Connections from DQM in many cases require a JDBC driver where virtually all would be type-4 drivers that have no dynamic library dependencies. Should you not have placed copies of the JDBC driver JAR files in <cognos>\drivers you will receive an error from the Java Run Time Environment (JRE) indicating that it could not load the Java class that implements the JDBC driver for the applicable vendor.
The video you referenced is showing how to define connections which are JDBC based.
When Cognos 10.1.1 was released, it provided a connection editor for five products (Db2, Teradata, ORACLE, SQL Server and Netezza) where you could define the connection information for either CQM, DQM or both. When you test those connections (i.e in the original admin portal, you will see that unless specified it will attempt to test both the CQM and DQM connections. As of 10.2.0, all other data sources supported via JDBC did not use the 'dual tabbed' connection UI and instead used the JDBC connection editor for DQM.
Many data sources have been added since 10.2.x where those products are only integrated and supported with DQM (i.e Amazon Redshift, Cloudera Impala, Google BigQuery etc).
Given you mentioned Db2 specifically, connections using the Db2 editor require the IBM JCC driver when using DQM. IBM JCC would be used for connections to DB2 Z, DB2 Luw, BigSQL and the dashDB (renamed to Db2 Cloud etc) engines. Connections to Db2 iSeries would use the JT400 JDBC driver they provide for Db2 iSeries.