Not all families are composed of individuals who are biologically related to each other. In many cases, those relationships are extremely important to the individuals involved.
DNA does not track those relationships where the connection is not biological. For that reason, when it is known that two members in a family are not biologically related, it’s important for the genealogist to clarify the relationship in their database as much as possible (adopted, foster, step, etc.) to help with the DNA analysis. It’s also important to document what is known about that non-biological relationship because it mattered (or matters) to the individuals involved and can impact their lives and records in which they appear together.
An ancestor of mine in Massachusetts was raised by a neighbor (after the parents died) and that neighbor left the ancestor a significant portion of his property when he died. There does not appear to be any biological relationship between the two, but I do wish I knew a little more about their relationship.
DNA analysis can be difficult enough. Try and reduce that confusion by clearly tracking in your database which relationships are biological and which ones are not.