Or they may have well not fully known what pronouns are preferred, and to avoid offending anyone chose the neutral, non-offensive "they", a universally accepted pronoun that could apply to anyone.

Regardless, you're getting offended over nothing because they is a preferred pronoun for Elliot, along with he.

Truthfully his "he/they" seems like when some trans people say that to accommodate cis people, not a genuine statement of identity.

This is pretty fucking disrespectful towards Elliot. Don't disrespect someone's preferred pronouns like that, that's even worse than your accusation.