Well spying... I'd say certainly not but of course, that depends on the definition. As you've figured out, after each update it does report some info that is relevant to the updater and the license checker. But nothing personal -- after all, you used some sniffer to see what's being sent and I'm sure you can confirm that it does not contain any info of personal nature. Stuff like IP address and computer name is something one can find e.g. in headers of your emails (unless you've managed to suppress it)...
BTW the GUID is avast's own GUID. I.e. upon installation, avast generates a GUID and reports it back so that we can trace the updating chain for a given installation -- particularly useful for tracking down updating problems...
Hope this helps,
Vlk