Some autistics have an odd view on what a special interest within autism actually is, and it's a very damaging take.
Special interests within autism can cause clinically significant impairments in one's life.
Special interests can borderline obsession and addiction and compulsion. They can even run inline with addiction, obsession, and compulsion.
Special interests aren't always knowing everything about it, researching it, and infodumping, or engaging in it in multiple ways.
Sometimes autistics don't know much about them, some will not research them, some autistics won't infodump about them. Some autistics only every engage in their interest in a very restricted and fixated way, a very limited way.
I honestly think some autistics get special interests and hobbies mixed up. You are allowed to have hobbies you are very passionate about, love to talk about, and have a vast knowledge on them. There are many allistics in this world who have hobbies just like that and with such an intensity.
Special interests for autistics aren't always cute and quirky and fun. They can be damaging and impairing, and cause stress/anxiety. They can be inappropriate, dangerous, or bad.