The interior's probably based on a shinkansen, with the A/B/C and row number printed above the window like this. The specific window style also fits these trains. Plus, given the business trip context, he's probably not going anywhere local.

That said, I'm not a train expert. Maybe some other non-shinkansen trains use the same interior style. Still, I'd bet good money on it being a shinkansen.

Part of the reason I'm pointing this out is because train interiors get redesigned. In two decades, who knows if the shinkansen will still look like this. Better to add context now.

Train nerd here. Yes, that is a shinkansen. You can tell by:
1. The lip at the bottom of the window.
2. The pull-down shade on the top of the window.
3. The row numbering above the window.
Considering that the row numbering includes three seats, it would have to be the ordinary seating car, not Green car.