You don't need to know who developed the LLM - whether it was Google or OpenAI.
What you need to know is who is the provider for the LLM, and whether their endpoints are zero data retention enabled and opted out of training. OpenRouter gives you an easy way to control this.
How can openrouter control what LLM provider does with your data on their side?
This is not entirely true and ignoring a couple of potential attack vectors like Data Poisoning: https://arxiv.org/abs/2408.12798
Its of course highly dependant on the use case and the environment, but simply saying that the only important part is to know where the data goes is too simple.