Internet speeds don't add
There is nothing wrong here.

Cyberduck &amp; LibreOffice downloads are displaying their average speed since the beginning of the real download operation.

Activity Monitor is displaying an instantaneous speed which will take into account these 2 downloads, but also all the background network traffic your Mac is always doing (ex.: netbios, Bonjour, ntp). This instantaneous speed is highly variable and depend mostly of this background network traffic.