ACI 302 and slump

I was pointed to ACI 302 and have read portions of it with interest. My 2 in. not-on-grade 7 pea gravel mix residential slab was 6 in. slump per the receipt I have from the concrete mix company. I was told slump should not be more than 3 in., but if I'm reading 302 correctly, it should not be more than 5 in. Either way, 6 is higher. (Note the mix was transported probably 1.5 hours to my site but I can't find anything that suggests this should require a higher-than-stated slump mix.)

And apparently too much water (higher slump) can cause excessive cracking, which I have experienced.

My question is, is ACI 302 *recommended guidelines* or "industry standards*? If guidelines, I'd interpret them as recommendations but if a contractor chooses to ignore, he/she wouldn't then be liable. If a code or standard, it seems to me a contractor would be negligent if they didn't follow this. Thus my question.

(See Table 6.2.1 in ACI 302-96.)

I'm also curious what exactly "seven pea gravel mix" is or means.