There are hundreds of ways it could have happened, yes.
Some of them are confusing mechanics, some are exploits, some are known bugs/issues that were never fixed, etc... But in essence, there's usually somewhere where you might have failed with security.
i.e.:
If the claim ends on the same tile as the walls (that is, the claim doesn't go beyond the walls), there are ways you can abuse this;
If there was any gap inside the claim, even inside the walls, there are ways this can be abused;
If any mineholes were not protected/secured properly, there are ways this can be abused
If you use field cairns, there might be a chance some of them were exploitable (like a field cairn that covers a wall and has vandalism for whites;)
If there are p-claims touching/covering walls, it's also possible that perms came from them and/or if the player was inactive (for example) it could've run out of Presence;
Finally, I've even seen some people mess up with village perms and let a wall fall by accident
And as people mentioned, there are tons of other possibilities, from ill intended or misinformed villagers to... things beyond

For example, there was a hermit near us that was raided when a "friendly neighbor" PM'd him and innocently asked for party perms "really quick" to "fix a road". Yes, raiders can be
that cheap - but it's also our responsibility to watch out for those things.
So... What I mean is: I'm sorry it happened but there are so many ways that it could've happened that the only way to truly be able to figure it out is if we get a bit more of information, especially screenshots of the breached points (with visible claims)

If you'd prefer, you can send them through PMs and I can take a look
