Is this a boundary or am I running away?

Here's a strange thing about boundaries and avoidance: from the outside, they can look exactly the same. Both involve distance. Both involve saying less than you used to, or seeing someone less than you used to. The person on the receiving end often can't tell which one it is, and honestly, sometimes neither can the person doing it.

One is aimed at protection, the other at escape

A real boundary is usually specific: this behavior, not that person entirely. It says, here's what I need in order to stay in relationship with you safely. Running away tends to be broader and vaguer, a general retreat from discomfort rather than a specific line drawn around a specific problem. If you can't quite name what you're protecting yourself from, that's worth noticing. Boundaries usually know exactly what they're for.

Notice whether you'd explain it if asked

A boundary can usually survive being spoken out loud. I need you to stop bringing that up in front of my family is a sentence you could say to the person's face, calmly, and mean it. Avoidance often can't be said out loud without feeling exposed, because the truth underneath it isn't really about a specific behavior, it's I don't want to deal with this, or I'm scared of the conversation. That's not shameful, it's just a different thing than a boundary, and worth being honest with yourself about which one you're actually doing.

Check what happens when the anxiety passes

Try this test: imagine the distance you've created, and then imagine the conversation became easy and safe tomorrow, no risk at all. Would you want to reconnect? If the answer is yes, this is probably a boundary responding to something specific that needs to change first. If the honest answer is still no, not particularly, that's worth sitting with. It might mean the relationship itself, not just this one issue, is the actual question.

Avoidance isn't a moral failure, it's just incomplete

None of this is about guilt. Avoiding a hard conversation is one of the most human things there is, and almost everyone does it sometimes. The only real cost is that avoidance doesn't resolve anything, it just postpones it, usually while quietly growing. A boundary, even an uncomfortable one to state, actually moves things forward. That's really the whole distinguishing test: does this distance move something forward, or does it just put it off.

It's alright if it's a bit of both

Most real situations aren't purely one or the other. You can be protecting yourself with a real boundary and also, honestly, relieved to have an excuse not to have the harder conversation yet. Naming both parts, instead of pretending it's cleanly one or the other, is usually more useful than forcing yourself into a tidy category.