It does respect robots.txt, but that doesn’t mean it won’t index the content hidden behind robots.txt. That file is context dependent. Here’s an example.
Site X has a link to sitemap.html on the front page and it is blocked inside robots.txt. When Google crawler visits site X it will first load robots.txt and will follow its instructions and will skip sitemap.html.
Now there’s site Y and it also links to sitemap.html on X. Well, in this context the active robots.txt file is from Y and it doesn’t block anything on X (and it cannot), so now the crawler has the green light to fetch sitemap.html.
It does respect robots.txt, but that doesn’t mean it won’t index the content hidden behind robots.txt. That file is context dependent. Here’s an example.
Site X has a link to sitemap.html on the front page and it is blocked inside robots.txt. When Google crawler visits site X it will first load robots.txt and will follow its instructions and will skip sitemap.html.
Now there’s site Y and it also links to sitemap.html on X. Well, in this context the active robots.txt file is from Y and it doesn’t block anything on X (and it cannot), so now the crawler has the green light to fetch sitemap.html.
This behaviour is intentional.