How does cache work?

When I look in the code, cache tags are added (in tooltip_taxonomy.module) and invalidated (in the forms).

Nevertheless, when I put a break point inside function tooltip_taxonomy_entity_display_build_alter, it is triggered whenever I refresh my node/ page, and addTooltip is being called multiple times, and $new_text is added to the $build array.

Am I correct that no caching takes place?