It's directed primarily towards Uighurs, but there are other minorities in the province. There are around 11 million Uighurs, around 1.5 to 2 million Kazakhs, and another one million Hui, who are Chinese Muslims who live in the province. Those three populations of Uighurs, Kazakhs and Hui are now subject to the potential detention, the Hui much less so because they're not seen as an existential threat in any sort of way. They speak Chinese and they're quite assimilated into the mainstream population in most cases.
Uighurs and Kazakhs are seen as a threat to some extent because they have territorial claims to the land, or at least they feel they do. They have been granted autonomy in the past, and they also speak a Turkic language as their first language, so they're seen as radically different.
They also appear phenotypically different in terms of their racial profile—in the Chinese discourse, at least—so they're seen as a distinct group that's different from the Han majority, whereas Hui can blend into the Han majority.