
It honestly just occurred to me, why did Goku use to say that sort of thing to Gohan?
Of course this is just Toriyama sloppily introducing this to reinforce Piccolo Jr. not being as evil as the previous Piccolo, but i'm wondering from an in-universe perspective, what made Goku think this way? As far as he saw Piccolo was irrevocably evil, he tried to murder everyone on the island, including his friends, multiple times in the Tournament, was overjoyed with the people being terrified of him, and even monologued about how great being evil and not having to care about people is, what hints would Goku pick up during or after the Tournament that this wasn't the same level of evilness as the original demon king?
Also, before he even mentioned that, he already had a change in his attitude regarding Piccolo Jr. from the beginning, with Piccolo Daimao he utterly hated the guy, and was always decided to kill him in cold blood, while with Jr. he is content with letting him live and has sort of a rivalry dynamic rather than pure hatred, of course this is largely because 1. he now knows killing Piccolo would cause Kami to die, someone he apparently cares about, on top of the permanent loss of the Dragon Balls, and 2. the fact that he is calmer now as an adult, not in grief over Krillin and Roshi's deaths, so this could be something that influenced Goku to think this Piccolo wasn't as bad, as he didin't actually hurt Goku's feelings much more than what the old Piccolo did, but i'm not sure that was everything, there must have been something that convinced him this wasn't the same level of evil, something important enough that he would comment on this to his son, who doesn't even know these events personally.
Was it something he noticed during the 23rd Budokai, or was it something he realized during the 5 years of peace? Maybe it was the fact that Piccolo never stormed into his house randomly to fight??
Personally i find it really interesting how his attitude with Piccolo Daimao is almost completely different from how he treats the younger Piccolo.