Though, I agree with what you have said, I think it might be helpful to look at the definition of justice and just.
Merriam Webster:
Justice (noun)
1 a : the maintenance or administration of what is just especially by the impartial adjustment of conflicting claims or the assignment of merited rewards or punishments
b : judge
c : the administration of law; especially : the establishment or determination of rights according to the rules of law or equity
2 a : the quality of being just, impartial, or fair
b (1) : the principle or ideal of just dealing or right action (2) : conformity to this principle or ideal : righteousness
c : the quality of conforming to law
3: conformity to truth, fact, or reason : correctness
and maybe the word just also.
just (adjective)
1 a : having a basis in or conforming to fact or reason : reasonable
b archaic : faithful to an original
c : conforming to a standard of correctness : proper
2 a (1) : acting or being in conformity with what is morally upright or good : righteous (2) : being what is merited : deserved
b : legally correct : lawful
I believe the meaning usually assigned to "Social Justice" is related to definition 1a of Justice and 2a (1) of the Just (or possibly 1a). People are making a moral judgement (or stating what they think is reasonable), which may or may not be tied to any legal precept.
So, the gp may, in fact, be using "Social Justice" is a consistent way that happens to match his morals or reason.