Yoricks mist walkers and maiden of mist apply lifesteal?

i was looking at yorick's abilities on his wiki page to see if there wan anything i could use to my advantage and under both his passive and his ult it said this; "Attacks from Mist Walkers will apply Life steal but do not apply on-hit effects." and for his ult "Attacks from the Maiden will apply Life steal but do not apply on-hit effect." does anyone know exactly what this means? if i was to build full lifesteal yorick what would be happening?