It just means that of the tens of millions of people who have had the vaccine, there are cases where people have died at some point in the time following.
But if you just took tens of millions of people on any given day, vaccine or no, the chances that some would die that day are high. It doesn't mean it was from the vaccine. It's just that with that number of people, you are going to get incidences of things happening that don't happen terribly often. And because people are actively looking for connections, they assume that it must be because of the vaccine. Vaccine makers are being ultra ultra cautious, so they will investigate every possibility, even when it's nothing to do with that.
Imagine how strange it would be if tens of millions of people had a vaccine, and nobody died that day. It would be hailed as a miracle cure for everything, because realistically, some people are going to die of random things on a particular day, regardless of what they did or didn't do.
There probably have been some really good but very rare things that happened to people on the day they had the vaccine as well. Those aren't reported or investigated, because it's not what people are worrying about or looking for.
You've done the right thing by having the vaccine, and have reduced your own chances of dying and reduced the chances of those around you, which is definitely positive. Feel proud that you've played a small part in ending this!