Buying to cover is not the same as simply buying. Buying to cover explicitly closes a short. Buying while shorting is called "shorting against the box" which I don't think many brokers allow anymore because it was mostly used for tax avoidance/fraud.
The articles give the impression that it might be better to cover with your own order rather than getting margin calls because the broker will try to close immediately, taking whatever order is available while you might try to slowly work orders to exit your position.
It doesn't matter either way, if the market moves rapidly against you, you're probably looking at the same terrible losses.