Question regarding Layout of W5500-EVB-Pico

TCP/IP Chip W5500
1

While layouting my W5500 board I came accros the W5500-EVB-Pico.

I was really suprised about the Layout especially the RXN/RXP and TXN/TXP pairs…
2023-03-23_07_03_11-GerbView

  1. TX pair is routed from back to top over vias, I thought that should be avoided at almost any cost
    Vias are not so bad after all?!

  2. the pairs look so tiny, how can they be have a Zdiff of 100 Ohms ? When I calculate the dimensions of a pair with 100 Ohms on a 0.8 2-Layer board my track width is almost a 1 mm