Going by the original thread, I have a few issues that I would like to be answered here before I give my opinion about this.
The attack is called a beam of light by the person. I don't see any other reliable sources saying that it is lightspeed? If there are, I think they should be provided. Because just being called a "beam of light" isn't proof on its own, as you can gather by many other such beams that are called light like piccolo's makankosappo, ginyu's change beam, freeza's death beam and so on. That's why our standards are there.
A supporting point was brought up that it got reflected off a metal surface. We see smoke rising from it and a character statement that says he deflected/repelled it. I mean, sure it got deflected, but nobody would have made this argument if he deflected/repelled it with his hands instead, or just swatted it away like a fly. Or if he had a different weapon in his hand instead of a metal. The statement "you deflected/repelled by attack" would still be valid in that case, and the feat would have been played out the same way. I don't think the reflection point is a strong point in favor of the feat. But even if we consider this as valid, it is still only one criteria, so I am not gonna argue this point in detail.
I believe the argument about the sfx is a valid concern, since the previous thread said that it did not explode, just burned. And while the "klang" sound was addressed, the sfx was not. I don't think real light would produce a sound, but let's wait for the translation to be 100% sure, since it is an important point.