From which website?
There have been numerous reports of Northern Guards inventing their own rules. The problem is endemic.
I do not know what Northern's policy is, but the Guard may not have been simply making up their own rules.
A policy at another TOC, briefed to staff says:
"A new procedure is being introduced that will permit colleagues to authorise customers to travel when prepaid ticket collection is unavailable.
How will it work?
A new TOD Issue Form will be made available at stations .... Once completed, this form may be carried by passenger(s) to substitute unavailable tickets. The form should be presented alongside a valid proof of purchase throughout their journey. Conductors and revenue protection staff will be briefed on the process.
Customers must present an acceptable proof of purchase such as an email confirmation (whether printed or displayed on a smart phone) in order to receive authorisation for travel. A booking reference on its own is not an acceptable proof of purchase and travel can only be authorised for XXX TOC services. "
Of note is that this form and policy only applies to the TOC in question, and not other TOCs that may call at stations managed by that TOC or for connecting trains with different TOCs."
So, if Northern staff have been told something similar then it may not be that the Guard is just making things up, but simply doing as he has been told.
Whether management have issued the correct instructions in the first place is, of course, an entirely different matter.
And of course, don't forget that the NRCoT does say in respect of boarding without a valid ticket "
...Where you are specifically permitted to board a train service by an authorised member of staff or notice of the Train Company whose service you intend to board..."
There has also been differing advice to staff over the years in relation to reference numbers and walk-up ticket types, so again, whilst I am not saying that the Guard was correct in this instance (indeed it sounds like he wasn't), it will entirely depend on what instructions and information he has (or has not been) given by his employer - both in advance in respect of company policy, and on the day in respect of a message advising of a national or local problem.