There are no grounds for compensation under the applicable EU reg. You accepted to be rebooked and you travelled as booked, i.e. there is no relevant delay. Sorry - but I do understand your feeling that you feel mislead. Most likely LH270 was cancelled and subsequently reinstated. In a situation like this LH systems do not rebook pax back to the original flight. If you had approached LH days before departure or taken this up at check-in BAH you would most likely have been allowed to rebook back on LH270, but upon arrival at FRA it was most likely too late.