Considering the original question, what are the odds of that happening, all we need to know is the number of possible alternative combinations. if there are 500 alternatives, the odds are 1/500. But the variables affecting the number of possible alternatives are many.
The number of alternatives is debatable indefinitely so I submit that there is no specific numerical answer to the question, it must be treated as rhetorical. My answer is therefore: "slim".
[following analysis is just plain wrong - retained for historical purposes only] I did consider it interesting that the two activators in question have the same callsign prefix, indicating a home location in Wales [edit: wrong: one is Wales, the other Scotland]. The common availability of summits at various points values, some with winter bonus and others not, would suggest the profile of available summits for the two operators would be similar. I did not research the number of years or the number of activations by each operator. But if the number of years was identical or nearly so, I think these factors all reduce the odds of their scores being widely different. So my secondary answer is "slim, but not as improbable as it would be for activators in different parts of the UK, or indeed in different countries".
In the case of bonus points, the common 129 activations could be divided by the number of years of activations and it may well be that the dividend would be close to the number of relatively close summits attracting bonuses, so each operator activated each of those summits during every bonus period. Another narrowing of odds.
My two cents worth duly submitted.