How to understand part of the text from the book about HAS-A and IS-A?

Question

Java

For example, they write:
If you want to know if one entity extends another, check for compliance with IS-A.
The triangle is a shape.
A cat is a member of the cat family.
This will all be true until you check for compliance.
I didn't understand here.
And then they write:
These concepts are interconnected, but through inheritance. Such a relationship is expressed by the ratio HAS-A. Isn't it logical to say that the bathroom contains a bathtub? In other words, the bathroom class contains a reference to the Tub class but does not extend it.
As I understand it, IS-A is when the parent class is extended through extends to the child.
And HAS-A is when a reference to the Tub object is created inside the Bathroom class through new Tab ().
I'm right? But in the book just below, they write:
The bathroom (bathroom) contains a bath (Tub). But none of them inherits (extends) the other.
WHAT???