It doesn't mean that it will be used that way, but rather really to make it clear that Gary can pull literally anything out of his hat that the Enterprise can do, time travel included. Otherwise, why even feed us the "theory" in the first place.
To add mystery and tension to the character early in the episode. If Gary Seven revealed everything up front, the story loses the element of intrigue and character development. "Space Seed"
works in a similar fashion; Khan's true identity is only theory in the first act--nothing confirmed, so it adds mystery to a character who was compelling, but the full story was not revealed.
In G7's case, the early dialogue--from Spock's history notes & Scotty's theory to G7's vague replies about his mission were the mystery/threat set up for the audience. We do not really know much until he explains himself to Roberta late in the story, but at that point, it remains clear that time travel is not one of his
skills, despite his recognition of the Enterprise
being from the future. That last bit just as easily can imply G7's commanders have met other time travellers, but not necessarily have the technology to do the same.