Yep that's right. When you use .length on an array, it tells you the number of elements within that array. Length on a String is the number of chars. Technically a String is little more than a char, so you can decay it into one and pull the .length instead of .length() if you *really* wanted too (I personally say that's a waste :P).
I would suggest a different delimiter though. Space is fine for your current names, but what about names like
Dick Van Dyke? Using spaces you cannot separate the last name from the middle name. I'd suggest either comma or semi-colon delmited instead. Everything would be the same except for the character used to delimit and the use of the .split().
header('HTTP/1.1 420 Enhance Your Calm');