I think either you misunderstood the technician, or he/she wants to teach you a lesson. Shorting the battery terminals would be both dangerous and spectacular. The only computer that would become awakened is the one directly behind your eyes.

There have been posts on this topic before, and the recommendations were that you do not remove any connectors from the ECC; there is enough slack in the wires to pull it forward. Others discovered they needed a software reload at the dealer if the ECC was disconnected, even for a short time.