Canada

I do think the author used a bit of hyperbole at the end there with that statement, but I can see three ways it could negatively affect pensions outside of Alberta.

1. My understanding is that the law specifying how much a province gets if they withdraw is a bit vague. Alberta used the most possible optimistic interpretation to lay claim to over half the fund and would probably fail, but it's not entirely impossible that they get more than they deserve (and thus shortchanges everyone else).
2. Many of the CPP's investments are meant to be held for long, long periods of time (like a skyscraper in Australia that earns money through charging businesses rent). If they're forced to sell some of that in a short time period to hand Alberta a wad of cash, they might have to compromise and accept low-bids than they'd otherwise get if they could wait years to find the right buyer.
3. This is more minor and theoretical, but many great investment opportunities only show up once you're big enough that you can start buying private companies wholesale (this is how Warren Buffet makes most of his money). A smaller CPP will naturally have less of these investment opportunities and be forced to invest more in easily-accessible investment opportunities. Worth noting that any Alberta fund would also suffer from this same issue to a greater extent, and may be part of why existing Alberta public pension plans have under-performed relative to CPP.