Huawei is perceived as a problem because they are big in infrastructure.
Xiaomi does smartphones that run on Qualcomm chips and Android. Of course there are always games and tit-for-tat but on the face of it Xiaomi is rather innocuous and benefits US companies (and that's probably why it was removed from the US blacklist).
Xiaomi doesn't provide the kind of network infrastructure that Huawei does. So they don't have access to the kind of data that concerned us policymakers.
If everyone start using their phones, they kind of will. I would guess it's easier to spy on people when you own the hardware and OS. Maybe the infrastructure would allow broader spying but owning a big part of the smartphone market allows for more in-depth spying for those with Xiaomi phones.