I have no idea of the technicalities of loading maps & nav.data int the a/c systems but, how long have BAW been operating this flight through EINN ? - & the ground crew suddenly think that the a/c is on a European service & load the wrong data ?! It seems rather too simplistic an excuse, don't you think ?
I think you're misunderstanding what happened when. The maps were uploaded at LHR by gingers who possibly never looked right when getting on and so didn't notice the J config (didn't even notice they were on a A318). The euro maps got them happily to EINN when the crew noticed the wrong maps - it wasn't ground crew at EINN who uploaded the wrong maps.