Well, that is specifically mentioned in the ground regs. Re the Preston (and indeed other away fans) doing it, might just be harder to spot when they are only there once, U's fans likely to be in same spot every week. Or they could hold "an appropriate license"?
20 Save as set out in paragraph 17 above, no person (other than a person who holds an appropriate licence) may capture, log, record, transmit, play, issue, show or otherwise communicate (by digital or other means) any Material in relation to the Match, any players or other persons present in the Ground and/or the Ground, nor may they bring into the Ground or use within the Ground (or provide to, facilitate or otherwise assist another person to use within the Ground) any equipment or technology which is capable of capturing, logging, recording, transmitting, playing, issuing, showing or otherwise communicating (by digital or other means) any such Material.
21 The copyright, database rights and any other intellectual property rights in and to all Material that you produce at the Ground in relation to the Match, any players or other persons present in the Ground and/or the Ground (whether produced in breach of paragraph 20 above, or pursuant to paragraph 17 above, or otherwise) is hereby assigned (including by way of present assignment of future copyright pursuant to section 91 of the Copyright, Designs and Patents Act 1988) to the Club and the EFL. You further agree (if and whenever required to do so by the Club and/or the EFL) to promptly execute all instruments and do all things necessary to vest the right, title and interest in such rights to the Club and the EFL absolutely and with full title guarantee.
As someone who has in the past been on the end of lengthy legal threats from the EFL lawyers for having photos of action (and fixtures) on my old website, the EFL are generally v inflexible about anything like this, no matter how stupid the resriction is (could you imagine a gig venue threatening legal action against someone who publicised when a gig was on? No they would welcome the publicity - not the EFL).