When youre just saying the same old lines that you’ve become familiar with over the years like “yeah I’m from here, and I’m not Japanese, yeah I studied. Na Na, I’m not good” and so forth, of course that’s easy to sound natural. It’s your 1000th time saying it, and you know what’s coming next. What truly shows if you’re legit “like a native” is when you have to have a conversation about something new for the first time, and you keep that naturalness. どんなことについても臨機応変に話せるかどうかだね。I’d be impressed if an American had a podcast in Japanese. Where they rambled on. Not just this same old 自己紹介程度のセリフの繰り返し。