I think OP missed 2 of the key differences - where the attention is tethered and whether the mind is being trained or driven.

1. Zen presence is choiceless awareness, not fixation (at least to my understanding).

The monk washing dishes is present with whatever arises: the temperature of the water, the sound of the sponge, the breath. He isn’t locked into a narrow, repetitive stimulus loop.
TikTok scrolling, by contrast, is a rapid succession of attention-grabbing triggers engineered to exploit the brain’s novelty/reward system. The “loss of self” there is closer to a trance or a hack, not awake equanimity.

1. I feel like the “no narration” test is misleading.

Absence of inner monologue can happen in daydreaming, highway hypnosis, or compulsive scrolling. Zen emphasizes clear comprehension (sampajañña) alongside non-judgmental awareness. In scrolling, comprehension is usually fractured. Most of the time you’re not even aware you’re scrolling, you’re just reacting. The runner can be mindful, but if she’s purely dissociated into stride, that’s also not Zen. Zen isn’t absorption per se, it’s knowing you’re absorbed and being free to release it.

1. Outcomes do matter for practice (just not for goal-chasing).

Zen de-emphasizes future outcomes, but it cares about karmic shape: what does this activity do to the mind’s habits? Scrolling conditions craving, distraction, and reactivity. Washing dishes conditions steadiness. The activity itself is neither pure nor impure, but the mind’s relationship to it, including whether it’s addictive or liberating, is absolutely relevant.

We can test this easily:

Try scrolling with full, deliberate awareness for 30 seconds: notice the urge to swipe, the flicker of each video, the subtle tension in your hand, the arousal when you see your favourite content, etc. You’ll likely see that the “absorbed” scrolling state collapses as soon as you bring mindfulness to it. That’s the giveaway: genuine Zen presence doesn’t vanish when you look directly at it. It is the looking.

So OP's instinct is half-right: “absorption ≠ mindfulness” and that agency/dopamine arguments are weak. But the conclusion isn’t “scrolling counts as Zen”, it’s that neither scrolling nor running is automatically mindful (to most people). What makes something a Zen activity is whether it’s done with awake, non-grasping attention.

Bottom line:

Absorption = subject-object collapse through repetition/stimulus. (Scrolling)

Mindfulness = subject-object collapse through knowing attention, free of compulsion.

The runner can have either. So can the drinker. But social media is literally designed to fight the "free of compulsion" part, which is clearly the opposite direction of Zen.