It does seem to be a bug, as you would expect \\t to work, but it doesn't.
Here's a workaround using a "zero-width space" unicode character:
| <b>json2puml | <b>v22.214.171.124\n |
| Generated at | 25.03.2022 11:26:41 |
| Input List File | data\\<U+200B>ttspec\\inputlist.json |
| Definition Option | default |