In coop, neither of those achievements even remotely needs anything like a grenade jump. "That just happened" is a simple matter of letting the other guy play more aggressively than you. And "Speed Reader" is extremely easy if you just play it with a rather turbo gameplay style; even if you die a lot and take far more than 30 minutes of real-world time, your segmented time is likely to be under 30, which is what matters.

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However, it's probably best to just not go hunting achievements for their own sake.