Originally Posted by
VSLover
no it is not obvious. until one catches that he OP checked bags through to LHR.
and there are plenty of reasons one may book on two separate tickets such as the very common "i thought i'd be in dallas but had to be in chicago before so needed to book a separate ticket"
not very difficult to imagine other scenarios.
Perhaps the second sentence might have been a small clue: ”I was booked on a BA ticket to fly the outbound part of a trip ORD/DFW/LHR.”