The only reason I can think was it was not a through ticket, and I think as the OP has vanished that would be the reason. We know the risks if playing the game to save cost of not doing a through. For example I recently took an EX BRU-LHR-HKG on BA. I flew BA from LHR to BRU on a separate ticket, fully aware that if I didn’t make it to BRU on time that BA had every right to put me as a no show in BRU and give me no assistance rebooking. Smartly I left more than enough time.
Sometimes they do have a heart, my colleague recently did the same but he used a LoCo on the booking LHR to BRU, due to bad weather his flight got canned, and as luck would have it the BA flight BRU to LHR also got scrapped. He went to BA, explained that he could not get on at BRU as his flight to BRU earlier in the day had been cancelled, throw in some story about needed to be in BRU an hour just to sign some legal papers + show them his boarding pass for original non BA flight and they kindly booked him to HKG on the next flight, no cost. So he ended up going EX BRU without actually going to BRU ?