In your case, that site is built on Squarespace version 7.1.

In previous versions of the Squarespace platform (up to and including 7.0), each template had a distinct name and identifier. It could have customizations, layouts and/or features within it that might not be achievable in any other template. So users had to switch templates if they wanted such layouts/features.

But with Squarespace 7.1, which is what the site in question is built upon, there is no meaningful functional difference between the different templates. Every named template that is available is really just an initial arrangement of content, layout options and settings that can be changed. Consequently, any named template in 7.1 can be made to look like any other template in 7.1 by simply changing that content, layout options and settings.

Therefore, the template ID (in your case, 5c5a519771c10ba3470d8101) does not uniquely identify any particular 7.1 template, but does generally identify the template as being built upon Squarespace 7.1. One cannot reverse engineer the template ID by itself to discover what the original template was named which the user started from.

Brandon is correct. Squarespace 7.1 literally has no templates. You can use the controls and settings to change any site into any of the example designs.