This burner phone and your "real" phone are going to be easy to correlate retroactively based on the towers they are both hitting
Also this correlation could be done with stingray towers without bringing the cell carriers into the loop.
I don't think gp here is in china, but rather just offering their procedure for acquiring a burner phone.
If the legit phone goes off while the burner is on that's a pattern. If the legit phone goes off and (travel time / distance) elapses before burner appears (travel time / distance) away from the last legit ping that's a pattern. If the legit phone and burner phone hit the same towers at the same time more than 3 times that's a pattern. If the burner phone spends most of the time off (battery out, faraday cage etc) then the times it does connect are even stronger signals.
You need to generate a ton of "noise" data where both phones are hitting different towers at the same time on a constant basis; and never being together. Maybe mailing the burner phone on a regular basis between isolated locations that the real phone never goes to?
Cell tower data is incredibly powerful for tracking people.