If you didn't order a special meal then why on earth did you accept it and eat it? It was obviously a mistake that you were given it and you may well have deprived that person of their meal. You should have said that you hadn't ordered a special meal before tucking into it.

And no putting you in that seat was not them being nice to you - that seat was allocated to you (if you didn't choose it yourself) when you got your BP in DEL or did you think that LH/UA used magic powers to change your BP dring the flight?

As to compensation for the spilled coffee you were given a voucher and an apology and to me that is enough. It is annoying but it was an accident.

On a UA fllight I once had some gravy splatter on me and I was given 1k miles plus a bottle of champagne plus a personal apology from the pursar. It was an accident and they apologised and I left it at that.