Normal
Personally, I’d focus on what you learnt and how it shaped your motivations rather than the detail of the open day. By focusing on what you took from the open day, you will provide more unique aspects than just describing what everyone else would have experienced at an open day (which is pretty similar from firm to firm). I would avoid making general statements like “I got the opportunity to learn more about the firm” and “I met with trainees and lawyers” as this is pretty obvious and would be something anyone could say who attended the event.