Firstly ignore anything anyone else tells you he thinks/ does/ says, they might possibly have their own agenda.
Secondly, he clearly is okay with just being friendly and social, so leave it at that for a while. Don't keep messaging him and pestering him and saying 'he says, she says' etc, that will only irritate him.
thirdly if you really do like him and he really likes you then it will happen if you see one another regularly, and if it doesn't you need to accept that he only wants to be friends.
In any event take it slowly, stop being so obvious ( men like to chase a little sometimes rather than have it all dumped in their lap like a present) and let him do the chasing if he's interested and meanwhile just be nice, normal and friendly.
As for his erection men get erections all the time, it doesn't mean anything necessarily.
So chill, be his friend and see if he starts to take a romantic interest in you.