Yes, it's saying that the string concatenation and other outside-of-SQL business logic took 22ms, running in their custom TH1 scripting language. In 2016.

Update: Actually it looks like I was wrong about TH1: https://fossil-scm.org/home/doc/tip/www/th1.md

The timeline appears to be constructed by C code instead: https://www.fossil-scm.org/home/file?name=src/timeline.c&ci=...

Update 2: Here's the timeline code from September 2016: https://www.fossil-scm.org/home/file?name=src/timeline.c&ci=...

Back then it had some kind of special syntax for outputting HTML:

    sqlite3_snprintf(sizeof(zNm),zNm,"b%d",i);
    zBr = P(zNm);
    if( zBr && zBr[0] ){
      @ <p style='border:1px solid;background-color:%s(hash_color(zBr));'>
      @ %h(zBr) - %s(hash_color(zBr)) -
      @ Omnes nos quasi oves erravimus unusquisque in viam
      @ suam declinavit.</p>
      cnt++;
    }
  }

That @ syntax is used in modern day Fossil too. Maybe that adds some extra overhead?