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)
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)