Not quite right. Yes pool filter sand is fractured. The other thing that makes it filter sand is that it is graded to a uniform size. In this case a #20 sive. Proper filter sand should never get past the laterals and in to the pool. At least mine hasn't in 3 years.i have been using quickrete for 3 years with no issues. some sand will always come through the laterals. its the nature of the material and how its screened.
what makes pool filter sand pool filter sand is that its fractured. this creates sharp edges that allow it to pack together more closely. Masonry sand is round from being tumbled in the river. it can filter, but not as well as the sand with sharp edges.