No, that's not what it means. It really just varies from person to person, and we don't really know why. You'll get the same protection even if you have no side effects.
Here are some articles that go into a lot of detail about how the vaccine works but end up saying in the end, it doesn't mean anything about your immune system - sometimes people get side effects, sometimes they don't, but it still works. :)
It actually could mean you have a stronger immune system. A strong immune system is a balanced one that doesn't respond either too much or too little when it's needed. It could also mean absolutely nothing at all about the immune system. I mentioned on a prior post the vastly different responses my wife and I had to the vaccine. We both got the Moderna, and both shots I got a sore arm, worse the first shot, and nothing else. My wife is still sick from her 2d shot and also got sick from the first one, feeling just exhausted and drained and did nothing but sleep. I just did what I always do. I mentioned there that when we both get a cold or flu she tends to get much sicker for longer than I do. When we worked away from home, she often missed work, and I never missed a day. But I'm not healthier than she is. We both have our problems, but mine are far more severe, although medication had a lot to do with that so maybe I shouldn't really put myself out there since that happened as an exemplar, as I was much healthier before that happened. It is to say some people are just tougher than others. Some are more determined. Some probably do have different immune reactions. It's just baseball, and I wouldn't worry about it. Peace.
My guess is that a weak or absent reaction means you already have some immunity