I guess if he's INTp, then the people on his forums that he thinks are INTp are probably INTj.
And if that is true, then (among other things) this follows:

1. The socionic descriptions of INTjs and INTps are false and misleading.
2. The MBTI descriptions of the types are better than the socionic descriptions.
3. The socionic descriptions of J and P behaviour are totally false.
4. The descriptions of the quadras are false and probably also the whole idea of the quadras in its present state.
5. Many of the descriptions of the type relations are probably false.

So, what is more likely to be the case ... that it is true that SG is an INTp ... or that at least one of the statements 1, 2, 3, 4 and 5 is false? (You can't choose both options.)