The radio-stop system is a simple and dated alarm system still in wide use in Polish Railway.

This is more or less a VHF radio function to transmit a predefined sequence of tones on a given frequency. Something like a DCS code.
Any train that is in the range of transmission and receive that sequence will initiate immediate breaking.

If you are not a radio amateur, you can just buy old train VHF radio station that has that function build in After the recent incidents press reported that they are available for $50 or less.

Because of it's simplicity and availability those false alarms are happening quite often. Press in 2021 reported some 60 occurrences only within a month.

Also the effect were not that dramatic. Article says that in one of yesterdays incidents the false alarm was received by nine trains. Out of it five were moving. They stopped and after and a minute-long waiting (confirming lack of danger) continued their journey.

Two man were tracked down and arrested later on. No information about their Russian associations so far.

if 100 phones travel at similar speed together (a network service) - it is not a car, and lock does not apply ;-)