Ex boyfriend kept my belongings for 4.5 months, and didn’t return them until my birthday

TL:DR, my ex-boyfriend (who I had a really bad relationship with) kept my things in his flat for months, and didn’t return them until my birthday 4.5 months later. Was this a coincidence, am I overthinking things? What does this mean? How should I respond?

I (29F) left my ex-boyfriend (34M) back in mid-September, after being together for officially six months.There were some red flags: he would get angry at nothing, have mood swings, would get annoyed at what I thought was harmless behaviour, such as snapping if I checked my phone at the beginning credits of a movie. He cancelled our anniversary holiday the night before we were supposed to leave, despite the fact he had spent two weeks promising to book somewhere. He promised to book a spa trip to make up for cancelling the first trip, but then he cancelled that too. He would ruin social events with his bad moods such as when I met his mother for the first time. He got blind stinking drunk for 16 hours the day before he was supposed to meet my friends for the first time, and cancelled that 2 hours before we were all due to meet. He spent some days texting his ex-girlfriend when her dog died, sending her heart emojis and so on, it went as far that even she stopped responding to his texts. When I got upset over this, he broke up with me over this, before I started crying and said I was sorry. He would tell me that he felt trapped being with me, and when I said I could leave him to it, that he needed me in his life and couldn’t be alone. I tolerated six months of this shit, before I said enough was enough and I left him.

On the last day of Novemeber, we met for a coffee. I initiated it, saying we could gain closure and say goodbye. At this meeting, once we had found each other at a local spot, we made our way to a cafe. Here he started crying and said that he had missed me, that I was rare, and that my little twitches are something he does / thinks about every day. He began to cry and had to excuse himself from the table. But there was something about this which didn’t seem genuine, it felt like he had to work himself up to cry. I felt this because when I tried to dump him a few times while we were together, once he started to cry I would always apologise and drop the break up. He said that he would like to get back together but at a few levels below boyfriend and girlfriend. I said no. He said I was rare and would like me in his life, even as a friend but he didn’t want to get back together. I said ok, but I wasn’t interested in being friends. Before he left he tried to say again: “you’ve always got a friend in me, like Toy Story”, and I told him I didn’t want to hear it. I asked him to send my things back in the post. I followed up with him a week after this, and asked him to give me my things back, and he said he would when he had time.

Some weeks went by, until we got to the end of January. My birthday was on the 31st. On that day is when a box full of my things arrived. Why do you think he did this? Was it a pure coincidence that this box arrived on my birthday? Am I overthinking things?

(Luckily I was out of the country on a holiday for my birthday, but I had received a photo from my roommate that this box had arrived on this date. So if I had been at home, I would have seen it.)