Seems like the extreme sensitivity (down to -146dBm) is able to deal with the reflections there pretty well down there.
But: that's not Through-the-Earth. It's Within-The-Earth.
(I have no details regarding the used band, antenna nor exact setup)
What is the use/appeal?
You either can parametrize it for speed or for robustness - there are a lot of parameters to fine tune it. Also it's easy to switch even faster modes (that are not LoRa) by just sending a few SPI commands.
The documentation of the chips is stellar. There are good software libs around, also Zephyr supports a few of them.
Also Semtech is extremely hobbyist friendly.
If you want to play around with them: use LoRaWAN and The Things Networks. There are a lot of basestations around - at least in Europe.
Getting >30km links with a still a metric ton of SNR left pretty much the standard. Even with lightly obstructed LoS. I've seen experiments with balloons that hat >400km links with plenty to SNR left.
Practically: we are using a single LoRaWAN basestation to gather telemetry from a giant industry complex. No problem even if the sensors are placed deep in the basement.