You are correct, submitting XML sitemap to a search engine or search engine finding an .html sitemap is not a guarantee that search engine will crawl these pages. Although in my experience, they almost always get crawled, but not always indexed.
According to you all how can we differentiate between these two sitemaps?
I am not entirely sure what you are asking here. Is your question whether URLs in xml and html sitemap should be the same (or can they be different) or are you asking something else?
how can we differentiate between these two sitemaps?
The search engine will find them in different ways. The html sitemap is-- I assume-- visibly <a href... linked from many places on your site, so humans can easily find it. The xml sitemap is only linked from robots.txt, and/or located at the root where search engines might look for it on their own.
Either way, the sitemap is purely informational. If all pages are reachable via plain-text links-- the way google is always telling you to do  --then you don't really need an xml sitemap at all.