What you’re describing sounds similar to one of the common effects of Survival Stress Reaction (SSR), a collection of physiological and perceptual effects associated with extreme stress and closely tied to heart rate. Other effects include tunnel vision, auditory exclusion and deterioration of fine motor skills.
There is actually a scale that ties different effects to specific heart rate zones. It’s easy to see how perceived “slow motion time” would be a benefit as your brain is attempting to rapidly process crucial information and respond in a survival situation.
However, these effects usually only crop up when a real or perceived threat is causing the elevated heart rate and usually cannot be duplicated when exertion alone is used to achieve the same heart rate (although instructors keep trying). I often experience slow motion time during emergencies and combatives training where a threat is being believably simulated, but not so much during regular training.
I suppose it’s possible that for some reason your brain is somehow interpreting metabolic stress as survival stress and triggering some of the same reactions, but that’s just an uneducated guess on my part.
