I was diagnosed this year with relapsing-remitting MS. I had a relapse in 2012 where my face and left arm went numb (but I didn’t bother seeing my GP at the time as the numbness was initially in my face so I thought it was dental work playing up, e.g. my root canal tooth!)
This year I had the numbness again and a whole load of other sensory/pain symptoms on the whole of my left side. Like you I had an MRI which showed multiple brain lesions (some old, some newer) which at the time the neurologist and radiologist felt was highly suggestive of demyelination. At my second appointment with the neurologist (to discuss the MRI results), the neurologist also mentioned MS but he said that I would need to undergo some further tests to rule anything else out. So no definite diagnosis, despite having two attacks of MS (the one in 2012 and the one this year), plus brain lesions & demyelination.
In my case, they ran further tests (bloods & MRI of both brain and spine) and they need to do this as some things mimic MS symptoms while others also cause actual brain lesions (the things I’ve read are sarcoidis, lupus etc). Therefore having brain lesions plus a CIS doesn’t necessarily mean that it’s MS.
That said, perhaps your CIS affected your motor skills which is why they mentioned informing the DVLA? My symptoms are awful pain, numbness, pins & needles and mild spasms, none of which would affect my ability to drive - which is maybe why they didn’t ask me to tell the DVLA?
A few months ago I checked the NICE guidelines on MS and it recommended that clinicians raise the possibility of MS as early as possible with a patient whom they suspect of having MS. I guess this is why we were both told early on that it could be MS prior to any relevant tests being completed.
Good luck with it all.