Probably that your laptop has the www domain with the old IP in its cache and the domain without www was older or not in the cache, so it took the new one.

If you are on Windows you can try to run this command from the command line:
ipconfig /flushdns

I thought that usually the DNS cache of the PC would expire before the one of the ISP, but strangely it seems to take a long time to update by itself for some of you