I support this erratum (it is an erratum as I see it). Compare to the clarification on Elven Cloak:
Can cancel a strike keyed to one, two or more Wilderness.
Edit 2019-03-26: Rewrote my post because what I wrote here yesterday was partially nonsense.
Funny about Elven Cloak. I get why the statement about multiple symbols was made.
But for creatures, it seems like most (all?) of the "deep wilderness" creatures, and even Wild Fell Beast, actually include a separate limitation in the card text requiring multiple region type in the site path.
So, my thought is that you technically still key the creature to one region type, but that two symbols in the site path are also required.
Meaning, Elven Cloak could cancel Winged Cold Drake but Wild Fell Beast could not be an automatic attack at Framsburg (it cannot be played because 2 Shadow-lands in the site path are required").
Update: I think this was true in METW and METD, but then in MELE rules were added for keying to multiple region types. And the MELE double region type creatures (Giant Spiders, Non-Spider Giants, etc.) lost the site path requirement in their text.