Well after a period of time avast would stop giving update notifications for avast5 (assuming you missed the initial ones) as avast5 hasn’t had a program update in some time, e.g. since avast 6 was released. We also don’t know what version of avast 5.x.xxxx you were using, if that was a beta build, that to could be a factor.

I also don’t know if you have set the Program update to Manual, in which case you wouldn’t get any program update is available pop-up.

There is a subtle difference in that avast 4.8 is effectively obsolete and they are going to end support for that at some time (sooner rather than later) so they are pushing to get people to install avast6.