RCD Test Tripping next door

[bgec]

Hi to all The other day I found the fault on a ring main this was repaired and when I was testing the circuit (RCD Test) the neighbour came over and said that his RCD kept tripping I was confused When I tripped the RCD in the house with the test it tripped next door at the same time to me that is wrong
I will be honest I have not much experience with TT systems and this is a new one on me too

Thanks Guys

[Polmenna-Martin]

Are they sharing an earth spike or it is bonded to same water incoming pipe?
What sort of Ze did you get, could be spike fault and they are close together?