Yes :) There can be multiple implementations using the same specification and still be compatible. For example, the new "facelift" they talk about in the submission article would be a new implementation, but still compatible with the old one, as they would (publicly) mostly have the same interface, so they can still talk.

There are many IPFS and libp2p implementations already, and they mostly aim first to be compatible with each other, so even if they work differently inside, they can communicate.

Similarly as with BitTorrent where many clients implement the same specification and can therefore exchange data still, just like TCP or basically any protocol.