Which is half true. All of them are vulnerable to Spectre. So far as I've heard only Intel (and maybe ARM) are vulnerable to Meltdown, because Meltdown exploits the lack of security checks on speculative execution that only Intel implemented. It's ambiguous if ARM is vulnerable, I've only heard people saying either "maybe" or that they haven't validated that.

Edit: Elsewhere I found a link to ARMs page where they breakdown exactly which of their processors are vulnerable to both Metldown and Spectre and it looks like quite a few of them are vulnerable to one or both of them.