The manifold in the picture is definitely not cast.

It's tubular. The welds however look like they are mig welded, not tigged.
Mig welding is a cheap monkey way to weld and doesn't even come close to the strength of tig welding.

Usually if a manifold is tig-welded, they will heavily advertise it as such.

I'm just going by what it looks like to me, a closer look would be needed to be certain - a higher resolution picture close-up would help.

Usually you get what you pay for.