Public people in which country? In the world? Perhaps the highest number of public people live in the United States, and there the official language is English, and therefore devices in English by default. If in Russia, then, as a rule, public people also travel a lot, and from this, they often buy their smartphones abroad, since it is cheaper than in Russia, and sometimes you can buy some exclusive or simply not yet sold devices in Russia. Why, the smartphones of the popular Samsung Galaxy line for the American market even work much faster and more stable, as they are equipped with processors from Qualcomm, unlike the same smartphones that are sold in Russia, but which already have Exynos processors. Well, plus, perhaps just for coolness they put the English language in order to use the original firmware interface. Probably all other countries are guided by similar ideas. But there is definitely no visible trend in this. And even more so conspiracy.
Most of our public people, or in English "celebrity", are actors, singers, politicians and television stars. In public, they speak only Russian. And they speak very good and correct literary Russian. For them, the Russian language is not only a means of communication, but also a way to make money. For them, language is a sacred cow and a holy grail. Moreover, many, feeling their shortcomings, hire teachers for speech, recitation and rhetoric for their own money. Tell me - from what side do they need English? And even more so a smartphone (which is only a means of communication) in English? While working on television, I saw and communicated with most of the celebrities and did not see any smartphones in English. I don’t understand where the very idea arose that their communications would be in a foreign language.
Specify the statement of the question. From the point of view of the theory of probability, it is quite possible that the majority of public people are Chinese. If at the same time they live in America for the nth generation, then perhaps yes.
The English menu is usually put on the phone by people who want to tighten their language, or, conversely, who know it better than others. For example, scientists communicate completely in English.
The topic of your question is conspiracy theories. Do you seriously think that nowadays you can use English to be conspiratorial? For that matter, choose alphabets that are more difficult to Google on the fly.