Why is composition labelled as a subset of aggregation in some illustrations?

Referring to an Image I found online. It labels Composition as a subset of Aggregation.
As per my understanding Composition is a form of tight coupling like when we instantiate an object inside another object. While Aggregation is a form of loose coupling kind of like a Dependancy Injection. They both seem different so why would Composition be a subset of Aggregation?

Image:
https://algodaily.com/lessons/association-aggregation-composition-casting

Because it's historical state of the art an not true for UML 2.5. Aggregation as attribute of a Property is explained on p. 110 of UML 2.5:

>- none | Indicates that the Property has no aggregation semantics.
>- shared | Indicates that the Property has shared aggregation semantics. Precise semantics of shared aggregation varies by application area and modeler.
>- composite | Indicates that the Property is aggregated compositely, i.e., the composite object has responsibility for the existence and storage of the composed objects (see the definition of parts in 11.2.3).

So actually both stand side-by-side with shared having no semantics whatsoever. Former UML specs had some definition which made shared some kind of subset. But that is just history. Though, you don't get it out of people's heads.

Composition is a specialized form of aggregation. In composition, if the parent object is destroyed, then the child objects also cease to exist. Composition is actually a strong type of aggregation and is sometimes referred to as a “death” relationship.