As I understand it, the author wrote to Flock as they are the entity collecting the PII. Your analogy would only make sense if the author had written to Flock's customers (and even then it's a rather strained comparison).

> they are the entity collecting the PII

I'm not convinced this is the case. It might be equipment made by them, but does that necessarily mean they were ever even in possession of the data in question?

Would you ask the manufacturer of your oven what you ate for dinner last week? No, you're just using an appliance that they made.

In the case of Flock I don't think we have any evidence of whether Flock themselves ever hold or store any data produced by their devices when operated by a customer.