Hi!
I'd say it's completely fine to talk about the same sector in both questions - in fact, it can make your application feel more focused, as long as you add new depth rather than repeating yourself.
In the "Why firm?" answer, you'd frame the sector as one reason you're drawn to them (e.g. their reputation, clients, recent deals, etc.). Then in the sector-specific question, you'd go deeper and discuss the trends, opportunities, risks, and how the firm could respond.
You won't look limited unless you only talk about that sector across the entire application. Therefore, if you're concerned, I would briefly reference other appealing areas that they practice in - but keeping one consistent sector thread can make your motivations look intentional and genuine.
I hope that helps!
