I'm watching DBZ again as an adult, and when Bulma, Krillin & Gohan meet two medical namekians, these people help them find some dragon balls.
I remember namekian dragon balls were very big, but these ones can be held by hand.
Why are they small?
In episode 41, Bulma and crew are not on namek, and the 2 "medical namekians" are actually 2 different aliens.
They are playing a mind game on Krillin Gohan, and Bulma. The reason then, that the dragon balls are still "small" is because these aliens only had the memories of the 3 of them to go off of, so the earth dragonballs. In a couple more episodes when they finally reach Namek is the first time we find out about the larger namekian dragon balls.