It could be rust?

If that’s the case - good, bad, nothing to be concerned about?

I went looking, not a lot I could find but the folks at inspectopedia (the link below will take you to them) might be able to provide you with more guidance!

concrete with rust staining

As per Inspectopedia, could be a touch of red mould.

Like in a toilet? eww.

It looks more like this: https://www.basementsystemsusa.com/basement-waterproofing/french-drain/iron-bacteria.html but it isn’t slimy looking or feeling.

But does it give off a distinctive sulphur smell?

It's a problem in Quebec's Eastern Townships. See this Quebec government website for further information.

There is no smell to it but I can tell you that it appears that another layer of concrete was poured over the initial concrete since the concrete almost covers our floor framing.

Mags438, we have no bricks, red or not

Melissa, did you figure out what that red dust like appearance in your basement was? we have the same problem - in the basement of our ranch. how did you solve the issue?