Because that's a colloquial name given to a range of specific symptoms people experience, and it is in the DSM, covered by 1.e.:
> Often has difficulty organizing tasks and activities (e.g., difficulty managing
sequential tasks; difficulty keeping materials and belongings in order; messy,
disorganized work; has poor time management; fails to meet deadlines).
The DSM doesn't list all minutiae of every general problem.
Having a single symptom does not mean someone has the condition. The diagnostic criteria for the condition for which you took that quote (out of context) is more comprehensive. It’s not a simple matter of doing Ctrl+F on the DSM and seeing that something can be a symptom or something else.
This is more obvious when you start thinking of other conditions: Feelings of sadness are a symptom of depression, but not everyone who has feelings of sadness has depression.
The misuse and misinterpretation of the DSM has become commonplace in parallel with the use of therapy speak.
They did not bring the DSM into the conversation, someone else did. And the person you are responding to made no such conflation! They also made no such claim that "[having] a single symptom [means] someone has the condition." That might be how you decided to interpret what they said, but it is quite literally not what they said!
They simply stated that time blindness is a real issue and linked to an article which acknowledges exactly what you are describing: "Many people with ADHD struggle with a lesser-known but deeply frustrating sign called time blindness." (emphasis mine)
I'm really not, you've made an argument based on a semantic misunderstanding of my first response. I did not say "time blindness" was a condition, I said that people generally self-diagnose conditions, not just for those symptoms. I also described it as a set of symptoms in later comments.
> Often has difficulty organizing tasks and activities (e.g., difficulty managing sequential tasks; difficulty keeping materials and belongings in order; messy, disorganized work; has poor time management; fails to meet deadlines).
The DSM doesn't list all minutiae of every general problem.