I thought it was a basic understanding that unfamiliar people, events, places, etc _do_ look alike, because before you get sufficient experience and exposure, you don't have enough skill to know what features are important to focus on and which ones carry no information.
It's also worth considering what saying that implies to the people you're saying it to. Especially when said dismissively. I'm terrible at names, faces, voices, pretty much any way of telling people apart. But that's my problem, and I need to be careful not to push the burden of that problem onto the people around me.
The first one CAN also be troubling if you have had ample exposure to become familiar, and are indirectly admitting that you did not believe it to be an important skill to learn.
I'd say it's an ignorant thing to say in the way you say it. Like you said in this post, you just don't know the features to look out for when you're not familiar with them