That's not good. At least they stopped well short of each other.
Despite previously living in Kent I never got to ride on the RH&DR.
Presumably the line speed is 25mph?
Do you know if the single line is controlled with tokens, or are trains signalled on and off?
Unauthorised entry onto a SL is about as serious an incident as it gets, but it will be interesting to see whether the cause is systemic, or human failng...or even both.
We await the Safety Digest which RAIB will issue in a few weeks.
Linky
Cheers, BW