That is incorrect, I think you're confused about the difference between search engines and browsers. DuckDuckgo is a search engine, not a browser. If you don't believe me, search "what is duckduckgo". Every single response will tell you it's a search engine.
Who ever set up your mobile phone or tablet set DuckDuckGo to be the default search engine and it probably has an easy to access button. But when you click enter on whatever you're searching for, it will open a browser window, be it Chrome (Google), Firefox, Edge, Safari, etc.