That slide emphasizes the design mindset difference...both languages can be used for validation, and as well as SHACL can be used to describe, ShEx can also be used to constrain, however their rationale is different and the slide can help decide which one to use

Both languages can be used for describing and validating. A typical use case of SHACL is to define the expected shape of instances, e.g. for form layouts. Complex "molecules" of shapes can also be described in SHACL, e.g. using its compact syntax.