I think blockers are elements which can not automatically moving. For example, grumpy cropsies can auto move, that means they are not blocked.
Baby mushroom is block but adult mushroom is like a normal cropsie.
I don't think the grumpy cropsies are not blockers, just they are movable objects. (For the mushroom, I'm confused it is considered blocker or not.)
Licorice swirls, and candy bombs in Candy Crush Saga are considered blockers in that game even though they are movable because they can impede the player's progress to reach the goal. (Licorice swirl: Preventing striped candies effect and guarding some object such as jelly to make level harder, Candy bomb: If the candy bomb's timer reaches 0, the game is over and lose a life.)
When there is(are) grumpy cropsie(s) in the matches, these matches count as 0 cropsies which can possibly impede the progress to reach the goal.
And bombs, too. Bombs in the game reduce amount of collected cropsies. In other words, these can impede the progress, so the bombs can considered blockers as well, even though they are movable.
With only Bridge (Farm Heroes Saga) (no River), this element = Conveyer Belt* (Candy Crush Saga). You can see Level 887, this level have only Bridge no River, and we have a Conveyer Belt. For River, no ones can stand on it.
Normally, Bull and Poppy Flower are together, but some levels have only Bull (example Level 849).
That why we need classify these 4 elements separately.