I’ve seen that MSE article before and at best it is incomplete and at worst misleading.
It is only discussing the legal requirement to have a separate bank account for accounting purposes. It makes no mention at all that all those groups it lists along with sole trader are considered businesses by banks (and HMRC who require you to list them as such on a tax return) and most banks say that you can’t use a personal current account for business.
I’ve been through this with all the major banks and asked them when I set up myself as a sole trader (alongside my main employment) and there was only one who under their breath said that if (and only if) the payments in to the account looked like salary (i.e. only 1 or 2 a month) then it might be OK. They all without exception told me that personal accounts cannot be used for business including if you are a sole trader.