I'm in a similar position to you.
This person had pre-agreed plans. You don't even know what they ould have been, a pre-booked train/ flight? An appointment? People's lives aren't so flexible that they can just cancel anything at a moment's notice.
When i give tasks to my junior who is Gen Z and it's late in the day, my first questions will be: what time do you finish? Will you 100% be able to complete this today? If they aren't able to, I give the task to someone else. She's happy to stay late to complete something, but for me, it has to be her choice/ free will, I wouldn't force her.
You're a senior manager and you're probably one for a reason. Same for me. I love work, I live for it, I prioritise it over other plans. I genuinely love it, it gives me structure, predictability, reward, in a way that many other aspects of life don't.
As juniors, you and me would have stayed late to do the task, as we take pride in our work, want to get on, want to be seen as reliable, high-performing. Lots of other people don't have that mentality. They're happy to stay juniors/ mid-level. Work isn't a priority to them. From Gen Z, I'm yet to meet someone that prioritises work to a high degree, it´s rare.
As managers, we just have to learn to accept mediocrity. The vast majority of people come to work to be there 9-5, do their job well enough, get paid and go home. There's nothing inherently wrong with that. It's a skill to accept and work with people with a different attitude.
Many, many people never stay late, and still do a very good job, my company is a great example of that. In fact, companies need to learn to work efficiently and within given operating hours, rather than seeing being at 135% capacity as normal.
My MD might message me at 4pm with a question. She always starts with 'pick this up when free, no rush' and if I do reply outside my working hours, she will genuinely tell me off, 'you shouldn't be dealing with this during your time off'.
I see my role as a senior to protect and respect the juniors. If someone wants to be pushed, I'll push them, but I won't push anyone without consent.