Delta IT is notoriously buggy when it comes to meal service, especially on codeshares.

There will be a standard meal service after takeoff (probably some variation on chicken or pasta/vegetarian, and a frankly mediocre warm snack (I haven't flown from LHR recently, but I'd imagine it's the same/similar as AMS and CDG, which have been an "Asian chicken spring roll" or a "feta and spinach spring roll," both of which aren't great).