Logical models allow authors to define new structures representing arbitrary content. While profiles can only add new properties as formal extensions, logical models can add properties as standard elements with standard paths. Logical models have many uses, as described in the FHIR specification, but are often used to convey domain-specific concepts in a user-friendly manner. Authors often use logical models as a basis for defining formal profiles in FHIR.
Logical models are defined in FSH using the keyword Logical. The keywords Parent, Id, Title, and Description are OPTIONAL.
If no Parent is specified, the empty Base type is used as the default parent. Note that the Base type does not exist in FHIR R4, but both SUSHI and the FHIR IG Publisher have implemented special case logic to support Base in FHIR R4. Authors who wish to have top-level id and extension elements should use Element as the logical model's parent instead. Authors may also specify another logical model, a resource, or a complex datatype as a logical model's parent.

It states that Parent, Id, Title, and Description are OPTIONAL.
Only parent is optional the other three are SHOULD.
This is also not reflected in the example where ID is missing while it SHOULD be there.