Based on the current flutterings about the social media site formerly known as Twitter it would presumably be because virtually anything seen as pro-white is a hate symbol, as well as various seemingly innocuous things. The most notorious being the OK hand sign, largely because it being pushed as a white supremacist hand sign was literally started as a 4chan prank (dubbed "Operation OKKK") whose purpose was to make the sort of media types actively looking for hidden crypto-fascist signaling from people look like absolute loons by just bathing them in false positives.
For example, the numbers in your username manage not to be a hate symbol, but had they been 2316 instead of 2215 they would be a hate symbol according to ADL because W is the 23rd letter and P is the 16th, therefore 2316=WP=White Power.
Numbers that are hate symbols include: 100%, 109/110, 1-11, 12, 13, 13/52, 13/90, 14, 1423, 1488, 18, 211, 21-2-12, 23, 23/16, 28, 311, 318, 33/6, 38, 43, 5, 511, 737, 83, 88, and 9%.
I keep waiting for some modern neo-Nazi group to use the ASCII codes instead of position in the alphabet so that list can suddenly be much longer.