It's like synchronised martial arts. In the Dragon Ball FighterZ finals at Thaiger Uppercut 2018, two players who both ran Adult Gohan figured out that they were fighting with a similar set of tools.
When two hits collide like that, it's referred to as a "clash," and it's been around longer than you might think. It occurs when two opponents input moves of the same strength that occur on the same frame - for example, each character throws out a crouching medium attack.
In games like Street Fighter II, both characters would take damage and hitstun, but in games like Asuka 120% Burning Fest and now Dragon Ball FighterZ, the moves graze off each other, not doing any damage or interrupting the combo.
Clashes aren't just a mirror match-up occurrence either; as long as the attack hits on the same frame and is of the same strength, it clashes. YouTuber desk put together a video of several different clashes happening, including some neat ones using beam supers like the Kamehameha.
It also seems appropriate that a Dragon Ball game lets you clash beams and hits together, since those moments are often a highlight of the show. Re-enacting the beam-battle between Teen Gohan and Cell in a fighting game is always a solid plus in my book.