Yes, that’s right. There are probably several reasons for this. First, the text on YouTube is in characters. Second, if you only type Pinyin, how would it know which word you meant? Sure, it could guess, but then you might as well use a Pinyin input method and enter the characters directly anyway. I’m not sure when looking things up in Pinyin only would both work practically and be useful at the same time! If you’re not learning characters at all, you can either use a Pinyin input method and find the right character or use a dictionary. Remember, even if the results you find are people speaking, it actually searches through text, and Chinese text is in characters, not Pinyin.