While I understand and appreciate the article, the answer to your question is still conjecture - since questions interrupt the flow of life and the first consonant in Sanskrit is also the first letter which is formed by interrupting the flow of air/sound from our larynx, people decided to form interrogative words starting with k.

I feel you have placed the cause before effect.

The usual chain of events is making sounds > agreeing certain sounds mean specific things aka inventing words > then inventing symbols to depict words on permanent media aka writing.

Short interrogative words with k were probably easiest to invent for a species transitioning from not having a language to having one. Later, the people who formalized Sanskrit put k first on the consonant list.