I got to Peterborough station just AFTER the incident occurred, as I was catching 1145 Thameslink train down to Hitchin as I'd just missed the 1115.
IIRC, the Lumo was 3/4 of the way out of Platform 1, whilst MY Thameslink train was in Platform 2, and a LNER train was in Platform 3.
The Lumo...