1. This doesn’t indicate language is necessary for thought but rather that language is useful for refining thought. If anything it shows that some form of thought exists before it is articulated into language. I would assume inverse cases also exist, where articulation into language narrows a thought down into the vocabulary of a language.
2. I thought rare individuals who did not develop language abilities (e.g due to isolation) still had
memories of their time prior to thought. The most obvious example to me is Helen Keller, who writes about her time prior to meeting her teacher.
Helen Keller wrote about having memories of being something like a stimulus-response automata before language enabled her to be conscious and think. I think that example is actually in favour of language being required for thought, because she remembers a state of being before language where she wasn't really conscious and didn't really think. I don't see any particular reason why language would be required for memory formation, though.
2. I thought rare individuals who did not develop language abilities (e.g due to isolation) still had memories of their time prior to thought. The most obvious example to me is Helen Keller, who writes about her time prior to meeting her teacher.