From the description of the boots of striding and springing:
your speed isn’t reduced if you are encumbered
Two lines from the variant rule on encumbrance (emphasis not mine):
encumbered, which means your speed drops by 10 feet
heavily encumbered, which means your speed drops by 20 feet and you have disadvantage on ability checks, attack rolls, and saving throws that use Strength, Dexterity, or Constitution.
Are these both considered "encumbered" for the purposes of the boots, or are they intended to be two separate keywords/statuses, with the boots only affecting the first?
I am leaning towards the latter, as it would make more sense that the boots wouldn't negate the speed reduction of heavily encumbered while still leaving them with disadvantage on rolls. But is there an accepted interpretation, RAW or RAI?