There's an important aspect of this that's being ignored: The flavor description.
The italicized description of Frontline surge doesn't actually use the word "push" at all. For the GM to ignore the description of what the power does in-game and instead derives his descriptive understanding from a power's technical shorthand is ridiculous.
The power says that the opponent is "beat back", and I'm happy to let the OP and his GM argue about whether or not that's possible. But to skip past the Italics and make your call based on the word that WotC happened to choose for a specific effect is as silly as saying "The monster doesn't loose any hit points to your fireball because you burned him instead of hitting him with something."
It's really important to recognize that "push" is a mechanical term that means "cause to move away from you." It does not mean, literally, "put your shoulder against the target and shove."
That's why the above is so important. As arscott points out, this DM is making a call based on his narrative interpretation of the word "push." While power flavour text is not binding to the rules, it does illustrate that how the mechanical term can represent a range of narrative interpretations. That's what the OP's DM really ought to consider.