I assume most KDE Plasma installations by default have the Unit Converter Plasma Search plugin enabled - you can check if it is on your device in System Settings > Workspace section > Search > Plasma Search:
One of the features of the Unit Converter plugin is currency conversion within the Plasma Search box (e.g. open the Application Launcher and type “1 USD in EUR”, and you’ll get the answer) - that feature is enabled by fetching currency conversion rates from the sites you identified there.
Disabling that Plasma Search plugin should stop those sites from being contacted if that’s what you wish.
Hope that helps,