It's not clear in the article how exactly they discovered it, but by the text that mentions it, I do get the impression they just came across the SIM ports/cards themselves:

> internal tests at a secure facility found Romanian SIM cards inside the buses

But it could also have been that they put the entire bus in a giant Faraday cage (or similar) and tried to see if it emits anything. If they did that, then eSIM or SIM wouldn't have matter, nor where on the bus it was, they'd eventually see it. But if they just physically came across it, then maybe eSIMs would allow them to place them in less accessible areas. But then maybe that wouldn't matter anyways, if the SIM cards are permanently attached anyways.

Bottom line, hopefully wouldn't have made a difference.

Every road vehicle sold today has a sim card, most for diagnostics, some for remote control.