Earlier today, I noticed one of my tires had a blowout. Anyway, at first, I thought someone had slashed one of the tires. I proceeded to think of what I would like to do to said person if I caught them, let’s just say it involved causing them an excruciating amount of pain and was quite a cruel/brutal thought. As best as I can tell, I had no intention of acting on this thought and I had no suspect in mind anyway. In the end, it turned out it was just a random blowout.
When I was thinking someone may have slashed the tires, I had no suspect in mind, just a thought against the random person who might have done it. By this I mean, I was imagining if I caught the person responsible, not that I had a person in mind already or anything.
Was this a mortal sin to think this hateful thought towards an unknown person?
EDIT: I was just at Confession yesterday (I go weekly usually) and I know if I were to go back today, the Priest would probably say I was being Scrupulous.