After OH died in March writing cards was one of the hardest things, along with ticking the 'widow' box when renewing the car insurance. Our daughter was the first birthday, I went into Waitrose to buy her a card and flowers, sat on a bench by the checkpout to write it and burst into tears when I wrote 'from Mum', when I took it and the flowers round she didn't open it, she phoned me later to say she'd wanted to open it on her own. I've also had to train myself to say my and not our and to say I and not we. Hard but I'm getting there.
I doubt your neighbour even realises what he's done, don't fret over it.