Tinderbox uses underlying Apple frameworks to automatically create 'Smart' Links (also call Smart URLs) where URLs are detected in $Text. Automatic detection of such URLs is enabled by default. It can be disabled using Edit ▸ Substitutions ▸ Smart Links. The setting applies to the current note rather than per-note and only applies while the note is still selected: on losing focus the setting returns to the default 'on' state.
To control Smart Link creation more persistently, use the $SmartLinks attribute. This preserves state and can be inherited via prototypes, etc. Templates notes are configured in this manner via their prototype as such link creation is unwanted in a template context.
Unless disabled in the Edit ▸ Substitutions menu or $SmartLinks, if Tinderbox encounters a valid URL being typed or pasted into $Text is will create a usable Web links. Previously, these links only worked from within (the RTF of) $Text, but now any detected URLs are added as full Tinderbox links and may be seen/edited in the note's Browse Links pop-over.
From v9.1.0, when Tinderbox adopts a smart link found in $Text as a Tinderbox web link, it now gives sets the path of the new web link to *untitled (i.e. no (visible) link type).