What you did was not vandalism, but it was rude, since it violated the moral right of the other user to control the words associated with their authorship. When one contributes to the article space, one is explicitly relinquishing that right, because Wikipedia is a collective effort, but that does not hold for talk space content, particularly when it is signed.
And what you did was doubly rude because you acknowledge that your version was "preferable"; that is, it is conceivable that the other user prefers their version. They may be wrong to do so, but by editing their words directly you are denying them their right to an opinion. It is not surprising at all that your edit was reverted.
