What does it even mean to "get updates from China"?
Software these days is distributed and globalized in virtually every sense. Polestar is headquartered in Sweden and much of their software development is in the UK.
Volvo's ultimate owner is the same state-aligned Chinese conglomerate.
The question isn't "why ban Polestar", it is "why ban Polestar without banning Volvo". They are both headquartered in Sweden, they are both owned by the same conglomerate, and they are often even both manufactured in the same factories. So what makes them different enough to warrant banning only one of them?
Because Polestar isn't a household name in the US. Most people have no clue they are even selling Polestars here. Volvo is very well known brand that has been established in the US for many years. and most people don't know it's Chinese-owned now. If someone said "ban Volvo" people would actually stop and wonder WTF is going on. You say "ban some brand of Chinese EV that you've never heard of," people aren't really going to care that much.
From other comments where telemetry goes to, and possibly the level of remote control in the cars.
It appears to be a general ban on "connected vehicles" controlled from certain countries even if built in the US[1], so I would guess that Volvo does not meet the criteria for that.
The devs, in the UK or not, will do what it tells them to do.