Kanji is a derivative of older Mandarin character sets. That’s why they look alike. Modern Kanji is of course dissimilar, but the glyphs still look similar, so unless you know one of the other deeply, I wouldn’t find it odd for people unfamiliar with either to be able to tell some of them apart.

The example characters you’ve provided do look fairly similar to me, though I’m somewhat familiar with Kanji and can normally tell the difference.