It means that there are at least 9 BusinessFirst seats for sale and that the J bucket is all that's available for purchase based of your search. The other fare buckets (also BusinessFirst) have been zeroed out by Revenue Management in hopes of making the airline more cash (J is typically more expensive).
By the way, this is what I see for UA128 (GIG-IAH) on 5-16:
Available Cabins: J9, JN9, C9, D9, Z9, ZN9, P0, PN0, R0, RN0, IN0, I0, Y9, YN9, B9, M9, E9, U9, H9, HN0, Q0, V0, W0, S0, T0, L0, K0, G0, N0, XN0, X0
Are you connecting? If so, you may see a different apparent inventory.