I think they are referring to one of the showcased demos of Spore, of which the most prominent is the 2005 GDC one.

https://spore.fandom.com/wiki/Removed_features#Creature_Stage

Behavior of creatures

The behavior of the creatures also had more depth than the final game. In today’s Spore creatures rarely leave the perimeter of their nest, and possibly has a simpler ecosystem (until Space Stage). This feature was prominent in earlier versions, as in the footage of the 2005 version, small creatures hopped around, grazed, or simply wandered off with no nests for them.

I love Spore, but replaying it today I see how much is missing from making each stage really fleshed-out. Being honest, the Creature Stage is clearly what received the most attention, while subsequent Stages are not as fun.
A lot of it is to be attributed to Maxis and Will Wright: apparently much of what was shown in 2005 and 2006 was never really playable.
But things like this suggest a heavy involvement of the publisher as well:

During the SXSW 2007 demo, Will Wright said that the Aquatic Stage was on the verge of being cut. He also said that, if cut, the Aquatic Stage would be one of the first things to add via an expansion pack, though ultimately no such expansion was released.

There was a plan to add the Aquatic Stage into the full game via an expansion pack titled “The Depths”, although it was never publicly announced. except for one advertisement.