If a thesis committe member asks for changes in my thesis does that mean I'm not getting a PhD "summa cum laude"?
I can only speak about the German system, but here it is mostly standard that some relatively minor changes (often stylistic) are requested. Usually, that is done after the oral examination / defense and has absolutely no impact on the grade.


  If the reviewer requests for changes, does it mean that he did not
  give the best mark?


You cannot infer anything regarding your final grade from this. You should concentrate on your oral examination since that is more likely to impact your grade (if you botch it). If you are really anxious about the requested changes, ask your advisor informally if the requested changes indicate a lower grade. Your advisor will probably be able to alleviate your concerns easily.

Keep in mind that summa cum laude is a big achievement but ultimately it doesn't matter much for your future career. Your network and your publications are much more important and nobody can take them from you.