It's yet more grift from protestors who are more caught up in the idea of protesting
something rather than actually doing anything productive.
It's not a fantastic exhibit and was fairly mediocre when it opened (and it's only become even more obviously dated since). But the penguins are happy, it fits with guidelines set for the species and as
@dillotest0 quite rightly points out, controlled lighting that is specifically designed to replicate something more similar to their natural environments is quite clearly not a bad thing. Not to mention the obvious - London is nowhere near cold enough for them, so of course they are kept inside. As I'm sure we all know and have seen in other collections, it is standard for sub-polar species like Gentoo and King.
I have my own opinions on the aquarium as a whole (in an ideal world it would close and either Sea Life or another aquarium open somewhere more appropriate in the city) and that exhibit is to me pretty damn dreadful. But it still serves the penguins fairly well, and despite what Born Free continues to insist penguins to actually require different needs to humans.
I did hear yesterday that this protest in particular, when presented with the facts around BIAZA and EAZA standards, claimed that both those institutes are corrupt and part of some grand conspiracy to allow zoos to hold animals in inhumane conditions. Certainly someone like Packham knows that to be untrue, but they evidently don't care - it's no different to standard political grifting. Anything for attention, and anything to try and mislead the public
I suspect they will be at Regent's Park soon enough claiming it's cruel to keep Aye-ayes in the dark...