I have never used Edge, I didn't like it from the start, too much history with MS and Internet Explorer, not to even try it. When Edge went Chromium, that was just another reason not to use it, I don't know like Google Chrome either.
My guess on file size would be that it reflects any change/update to the main Avast Program and could well mean a slight difference in the stub installer file size.
I downloaded it again using the link in your post, the file sizes are both 217KB and the same 222,104 bytes figure. So no differences for me.
Now on the page that link is on has 3 Steps and Step 2 mentions, 'Click "YES" on the system dialog (as spelt on the text) Window to approve the start of your Avast installation.'
So I just wonder if this is the UAC popup that you got, I don't know, as I said I have never used the on-line-installation file.