Effectively when the BA agents access your account, they log into your account just as you would do using an “on behalf of” portal. This is common with a lot of companies , banks, insurance etc so that when you phone up with a query or problem the agents can try and replicate what you can see.

I had this when trying to chose a seat on a flight and the agent said I’ll just log into your account to have a look and see why thst isn’t coming up,for you... then selected the seat that I couldn’t but should have been able to and sent an investigation ticket off to their IT team.