That could be! I installed Office 2007, used it for a couple of days, and removed it. I went back to Office XP (2003) which I find far preferable because the toolbars aren't crowded with stuff that I'll never use.
I do indeed have the "plugin" that allows Office 2003 to read .docx and .xlsx files, so maybe that's what it's trying to update. I assumed it was looking for the Office 2007 that I zapped. Same difference
No idea about Avast. I just installed it, said "Yes" to everything, and let it get on with it. It works! I'm impressed, in fact - it caught another wriggly nasty today, trying to sneak in under the radar and pretending to be from my Bank.