What does it mean when plaque is outside the artery?

I just had a cardiac catheterization done. No major blockage, so no stent, just a catheterization.  The Dr. said there was plaque buildup on the outside of the artery, which causes it to bulge out, rather than the typical plaque buildup narrowing the artery.  Just had this done three days ago, and of course I was kind of fuzzy when he was explaining this.  Don't go for follow-up for a couple of weeks.  Also, they put me on Crestor, Plavix and metoprolol for blood pressure.  I've never had high blood pressure.  Even during stress test it only went up to 134/72.  One day last week it was 100/60!.  I am confused by putting me on medicine for high blood pressure.  What is the reason for this?

[Occupant]

I don't think plaque builds up on the outside of the arteries. It is just that sometimes the walls of the arteries bulge outward when plaque builds up rather than narrowing the Lumen. I can't comment on as to why they put you on Metoprolol, but I was on Toprol XL (Metoprolol Succinate) for a number of years and I am glad one cardiologist finally said: "Don't take it anymore."

[a_lake]

Thanks for the input.  As I said, I was still a little fuzzy when he explained it all.  I am definitely going to ask more questions at my follow-up.