The entity class termed the devil and his messengers DO have access to the minds and hearts of mankind.
Jesus showed this as a principle here:
Mark 4:15
And these are they by the way side,
where the word is sown; but when they have heard,
Satan cometh immediately, and taketh away the word that was sown
in their hearts.
It's only odd when believers don't understand that the tempter tempts internally, in mind. But it is a well established principle in the text. Most discount it by falsely equating it with Hollywood movie types of possession when that really isn't the equivalent comparison whatsoever.
Not every thought is our own.
Believers are the first ones in the line of attacks. That is why we are to be armed with the facts.