I know of no "spot spreads".
Rather, I referenced a spot position spread ... which is like any spread, however, one leg (long or short) involves the spot month.
Often, there are some interested in rolling their profitable position (in this case, probably a long) into a deferred month, therefore, generating more liquidity than an outright purchase (ie: you covering your short positions).
I've not heard the term "calendar spread" utilized in outright futures, thought it was more of some of that new fangled option terminology.