Just to hammer home the point, the key word in my sentence is "some". I'm not saying all, or even most, Leave voters were so cynical as to treat the 2016 referendum as a "two-fingers to Westminster" vote, but is it really so outrageous to suggest that maybe a tiny percentage of the turnout was less anti-EU and more anti-politics?
Results I can find in polls tend to suggest that the proportion of Leave voters who voted purely for anti-EU reasons is in the region of 90-95%, eg this one:
http://csi.nuff.ox.ac.uk/wp-content/uploads/2018/05/Carl_Reasons_Voting.pdf
You may also find these results quite interesting because they reveal that Remain voters as a whole seem not to "get" the motivations behind Leave voters very well, eg Remain voters tend to overestimate how important immigration was, and underestimate how important sovereignty was.