Twitter using Rails to grow to the point where Rails became the problem was actually Rails's selling point. If you ever grow to the point where Rails is your problem, then you have money to solve that problem. But if Twitter hasn't used Rails, they might not event get to the point where their product is out the door.

It's absolutely correct to say Twitter blamed their issues on Rails. It's less likely to be correct that they wouldn't need a similar major change if they had started with anything else and grew from an MVP to one of the busiest sites in the world. I personally find it doubtful that they couldn't have done it with Rails.