Do you get the Multimedia Fusion 2 engine even if you pay less than a dollar?

yes

Why humble let this to happen ?

Note that the version with this name is old 2.0 and if you want the current 2.5 with the slight name change they have a special you can upgrade for $39

Just tried.
And it worked. O.o'

But we are probably not getting Steam keys, if one of those games get Greenlit.

Unfortunantly I think so.. (but not the steamkey when/if that comes)

But on top of that you're also getting the unpleasant feeling of screwing over Humble, the devs and charities..

EDIT: No steamkey will be released for this title. I misread a message from HB, sorry about that.

Just pay the dollar, come on.

Sure, pay $0.01 and let Humble take care of the transaction fees, server maintenance and bandwidth.
You are a wonderful person.