Is this weird? (Buyer behavior)

I sold something a few weeks ago, shipped it, the buyer left a five star rating, I moved on with life. Today I go to the mailbox and there’s a handwritten card from that buyer thanking me for it.

Am I wrong to be a bit creeped out by this? It’s a business transaction. There’s no need to use my address after leaving a rating and accepting the offer.

ETA: no, the buyer was not an older person. Please stop saying "if it's a woman don't worry." I have literally been stalked by a woman before to the point of having to move and then she managed to stalk me in a different country lmao