How do you identify settling cracks versus structural cracks (new build )
Several things are occurring here: 1) cracks through the blocks not just mortar joints, 2) vertical and diagonal cracks

1) In construction, block walls are designed with mortar joints to be weaker than concrete blocks. That way, when the building settles (and all buildings settle) the wall will zig zag crack down the wall in the mortar joint, NOT through a block. Replacing a block is much harder that repointing the mortar. 

Your mason has screwed up and caused a big problem that can only be fixed by replacing the cracked blocks. 

2) Generally, vertical cracks are caused by the foundation settling in one location and a diagonal crack is caused by the foundation settling along many feet (big area).

They are both “structural” cracks, it’s just that one is a bigger deal than another. A small crack (like yours) is called a “hair-line” crack and is minor. Often the building is constructed so fast that the foundation does not have a chance to settle before the final finishes have been installed. I think this is what happened to you. 

I’d monitor it by drawing a line across the crack every 4’ or so, number the lines, and measure and photo each crack. I’d keep a journal for 1 year checking at regular intervals, say on the 1st of each month. If it continues to get bigger, you have a problem. 

Likewise, if any cracks develop, note and monitor it too. If crack gets to be more than 3/16”, you have s problem. Let your contractor know what you’re going to do and send him notes and pics each month. Let him know you expect the cracked blocks replaced at the end of 1 year, plus and walls with cracks larger than 3/16”. (Check your warranty and make sure you send certified letter before the warranty ends.  Maybe this will be a 10 month monitoring process instead of 1 year.)