RTL stylesheet automatically working

I am currently developing a theme which is rtl supported. As i noticed from some posts in the web, it should be enqueued after main style sheet. But even i have not enqueued rtl style sheet(rtl.css) it is automatically enqueued and working. when i change the site language to an rtl language from Settings > General everything is working perfectly. This is not because of browser cache.

I need to know is this normal? Is it not necessary to enqueue rtl.css?