I can’t tell what in the product description describes the dents, if it does at all, but I bought this board (it’s called “The Team” and made by Flow) for 100 bucks at sierrasnowboard.com and it has hundreds of tiny little dents in it, in an obvious pattern and obviously done on purpose.
My snowboard instructor had no idea what they were for. He didn’t really like them though…so he had me use a rental!
http://www.backcountryoutlet.com/outlet/FLO0051/Flow-The-Team-Freestyle-Snowboard.html?CMP_ID=SH_PRG002&CMP_SKU=FLO0051&mv_pc=r120
It’s supposed to give you less surface contact for more speed to hit park jumps and half pipe transitions, It has some great reviews but it says it’s for more advanced riders. I don’t know why your instructor didn’t like it though.