That's the IPv6 bypass we've guessed at.
That Macbook Pro is using an alternative DNS server via IPv6, bypassing Pi-hole. Thus it fails to resolve pi.hole (which is only known by Pi-hole) and doesn't block flurry.com.
You should configure your router to stop offering its own IPv6 address as DNS server, lest your devices will bypass Pi-hole via IPv6.
But let's not forget about IPv4 and check that as well.
I am not really fluent in Macs, but the following command should list DNS servers your Macbook Pro uses:
scutil --dns