Beautiful pipe Jim. I loved your comment that it may be a freehand but that doesn't mean hands free!
The term straight grain is always subjective to the smoker and maker. Companies do mark their pipes as 'straight grain' but that's their opinion and sometimes their opinion is well, prejuduced

. In a general sense, straight grains should be pipes where the grain flows from rim to heel in parallel straight lines. Flame grain usually connotes that the grain flows similarly but may be angled one way or another or both ways.
No two straight grains are the same and they vary in quality with the ideal being the tightest (least room between the grain) and straightest.
Your pipe was cut from plateaux briar (that's the burl exterior on the top of your pipe) that's usually the source of the best grain and it's often the most expensive cut of briar. The shape of the pipe affects the quality and amount of straight grain that can be expressed on the pipe. Your pipe was handmade to follow the contour of the grain. Had your block of wood been made into a billiard it would necessarily have had mixed grain around part of the bowl. You'll sometimes see the term, 360 degree straight grain that simply means that the owner feels that the straight grain goes all around the pipe.
Pete