Topics are simply links to pages, all the filtering is done on the destination, that is why you need to enable "Topic URL Filtering" on the destination channel.
In order to build the Topic URL (link) Affino checks the current section by default, so the link for the topic will be the same channel/section plus the topic screen name.
Example: affino.com/[channel/][section/][blue]
For more information, please refer to these FAQs: