I’m of the mindset that you bought the domain you can do with it as you please. Where I think you’d get into “trouble” is if you were talking about piracy or something associated with their IP.
And the best possible outcome is they contact you and buy it for some much larger amount than you paid for it.
I work for a small dev company. We have no idea what other silos are working on. Only 1-2 people at the very top have some sort of inkling… Maybe.
In a company that large… I don’t doubt that projects get filed under a very large encompassing epic (or the equivalent for what ever scrum software they are using) and not overly discussed with the business majors / marketing people that are the c-level people now.