Tidal bore surfing has been done since the 60's. Europe has a few like the Severn River in the UK.
The "homies" hyped it up with that explosion.
They are pretty predictable; look at the moon phase for the low tide and you can set your watch for a ridable wave. Only other possible thing was they waited for the movement of a large ship. I've seen a few real nice waves on the mud flats of the Delaware river from ship traffic.