That's because they question the backfill of the pool which is expected. The decking guy should be doing or supervising the backfill and stone should be used.
The biggest issue with concrete sub base is it WILL crack amd expand. Once you lay sand over it amd install pavers any cracks that make a void allows sand to settle amd in turn lets the pavers start "birdbaths" as we call them. Its good hes got rebar in the concrete, but a proper overlay requires some type of fabric over the slab to prevent that. That rebar needs to be bonded as well, fibermesh in the mix would have been a better choice. It's very important to have a uniform sub base and concrete sand thickness, you never want over an inch under the pavers, the final compact will settle them differently when doing your poly sand joints