I think you already know the answer:  Make the call.

Just because a center is a stroke center doesn't mean they know about moyamoya.  My husband's stroke neurologist at a very prestigious hospital was sure that what he was seeing was moyamoya syndrome from atherosclerosis because he was looking at a perfectly functional 58-year-old slightly overweight guy and congenital moyamoya is so rare.  Good thing his neurosurgeon knew differently after seeing his angiogram.

Make the call.  Have the latest MRI/MRA scans sent to Dr. Steinberg.  Maybe it's nothing.  Maybe it's something.  Don't be shy.  It's better to know than not know.  You are probably not looking at anything terribly serious, but I am a widow now because when my husband's EDAS incision site started looking bruised, his speech became slurred, and his hands started shaking on September 21, I didn't insist on calling his surgeon.  He didn't want to.  He had a stroke that night, then seizures that could not be broken and he never came back.  My crusade now is to make sure others don't ignore symptoms.  If my nagging saves one life it is worth it.

Make the call.  My thoughts will be with you.