Generally speaking, as I'm not a patent lawyer either, the same technique applied to two different problem domains can generate two valid patents. The historical example is ship and automobile windscreen wiper.
Not to argue with you, but I don't see the problem any different from trying to synchronize two commits in a database. The same technique is not limited to Spanner or algorithmic trading, but other fields as well. It's not so much different from DHT or other algorithms, which have applications in multiple domains.
You could argue ships and automobiles are in the same transportation-domain ?