DS had one too. She couldn't recognise an autism diagnosis on a sheet of NHS letter-headed paper.
He's the classic, shy, intelligent with a penchant for niche details type. The shorts every day of the year was the most obvious manifestation of his sensory processing disorder. Understandably she couldn't see the restraint release meltdowns at the end of the day, the termly cycles of exhaustion, the patterns of unusual behaviours since he was a young baby before he'd even seen CBeebies or before we owned smart phones or tablets. I don't know how she managed to insist that he enjoyed the music lessons with the shrill glockenspiels because the video panning the class showing him face down on the desk with hands clamped over his ears made him look pretty miserable. He wasn't allowed reasonable adjustments for his SATs because "he was doing well enough" despite 3 diagnosed conditions affecting his processing and writing speeds. (Oops, he didn't meet his targets because he was "anxious"... err... that why reasonable adjustments are supposed to be avaliable 🤦♀️)
Naturally months after the event too late to do anything he told me that his teacher didn't know that he's autistic and was surprised that he said he was...she was the fucking SENCO at the point he was diagnosed and I'd exchanged correspondence with her on the matter 🤦♀️
So yes, unfortunately I can believe that there are teachers this ignorant out there.
At school in the 90s, I hung out with the cluster of quiet, quirky "geeks". Some are now getting diagnosed in their 40s, others with the hindsight of better knowledge had clear traits of neurodiversity that were overlooked at the time which has meant that when people have struggled, those situations have been managed from the wrong angle. DH's family is full of older men who tick many autistic traits, and a younger generation meeting diagnostic thresholds. It's always been there, it's just being recognised more now, and modern living can often expose areas of difficulty in a busier, more complex, chaotic world with less routine and familiarity.
Putting a revelevant diagnosed difference or disability into an OP is often relevant because it makes more of the responses appropriate.
Recently diagnosed adults can often "special interest" or hyperfocus on their diagnosis too due to the nature of ND conditions.