It's not as black and white (pardon the pun) as "people who boo the knee are *only* booing because they are racist". There's a cross section of those that boo the knee and also sing the Diallo song, those will be the racist ones.
There's also some that will do one or the other: because they agree that anti-racism - the knee - is a good stand to take, but don't see the harm in the big dick song.
On the flip side, there's people that will boo the knee (because they believe it to be more a political organisation rather than anti racism), but will rightly recognise the racial stereotypes in the Amad song so won't sing it.
It's probably about clarity and getting those in the latter 2 scenarios to understand that 1) the knee doesn't represent a political organisation, it is a gesture of anti-racism. 2) The song isn't acceptable as it is based on racial stereotypes, that even the player himself has said is uncomfortable.
In addition to the last paragraph, immediately labelling anyone that does either of the latter two as racist is counter productive. The first group that do both are likely racist, however and probably wouldn't listen to any attempt at clarity or education