I would put money on this being a racist gesture made by an absolute cretin.
However, what I think newy is getting at is that until we see who it is aimed at how can the authorities deem it to be racist? We can’t act on something we can’t be sure of, even if it seems pretty damning.
If I was to play devils advocate and look for an alternative, however unlikely it is, shouting at someone resembling famous monkey chant receivers like Gareth Bale or Liam Gallagher, or a similar white person with perceived simian qualities, is not so far fetched to be utterly ludicrous, although it would take a special kind of stupid to make gestures like that at anyone knowing how it could turn out… I concede that the above is unlikely but for justice to be done we have to be in possession of all the facts.
Now before I get accused of downplaying or condoning anything, I’m not. I think the most likely scenario is a dim racist doing what dim racists do, and if proven the book should be thrown at her as it’s a thoroughly unacceptable way to behave.