Well, let's keep in mind it is decentralised, so only people who have been in contact with you can correlate it with your location at a given time in the past. Not the whole world nor a central authority.
And even is someone goes to that extent to track your identity down, I am not sure that local de-anonymisation is a problem. This is not something like HIV. I don't think there is any social stigma to catching the coronavirus. If you catch it you should self-isolate, and it will be obvious to the people around you that you got it. And if you don't want to self-isolate and want to hide it, what is the point to self declare that you got contaminated on the app in the first place?
And even is someone goes to that extent to track your identity down, I am not sure that local de-anonymisation is a problem. This is not something like HIV. I don't think there is any social stigma to catching the coronavirus. If you catch it you should self-isolate, and it will be obvious to the people around you that you got it. And if you don't want to self-isolate and want to hide it, what is the point to self declare that you got contaminated on the app in the first place?