I’m just some random guy with advice, I cannot observe accounts.
You don’t use particular models but they have usage → someone else is using your models.
Pretty straightforward.
Usually something bad in practice, like hard-coding API keys in code, easily committed to repos or seen by others, or having any client software connect to OpenAI instead of to your own backend, allowing extraction and discovery of keys.
See, for example, this discovery of bad implementation: