I'm not thinking prequel at all. Why think that?
As noted the 'net was a buzz that Coulson may not fully be dead. The idea that a cheat is being created should surprise no one.
I'll be disappointed if it is a prequel, there are so many more options with it running parallel to the MCU. Episodes can flashback, during and around the existing MCU. If it's a prequel they are largely stuck pre IM and TIH.