Grass blocks were previously in KillAllowed, which allowed you to bomb them and break them, potentially opening up unintended paths (I unintentionally used this to get to Tomb of Gwyn before the Hunter).
Keep in mind you couldn't mine them; mining them no matter the tool would just revert them to dirt blocks, which can't be broken (unless as a wall, of course). Bombs don't convert grass to dirt; they just break it directly.
With this, bombs & tools can still break a line of grass blocks, but bombs can no longer break grass along a surface.
Grass blocks were previously in KillAllowed, which allowed you to bomb them and break them, potentially opening up unintended paths (I unintentionally used this to get to Tomb of Gwyn before the Hunter). Keep in mind you couldn't mine them; mining them no matter the tool would just revert them to dirt blocks, which can't be broken (unless as a wall, of course). Bombs don't convert grass to dirt; they just break it directly. With this, bombs & tools can still break a line of grass blocks, but bombs can no longer break grass along a surface.