Those are all things that happened and I wish I had the links handy. Posey legitimately seems to support a bisexual Scott.
Here's an interview at the premiere of Pitch Perfect where he says (around the 3 minute mark) that in season 3, he'd like to see Scott become an alpha and make out with Dylan* for a change.
There’s also this interview at NYCC after the official panel where someone asks him a question about who he’d be in a relationship with on the show aside from Allison, around the 5:20 mark. He says that he thinks Scott is straight, and starts to muse about who he’d want Scott with if he were gay; he leans toward Scott/Stiles a bit, but he says that while Scott and Dylan* (which he then corrects to Stiles) already have a ~bromance~, it’d be weird to have them in a relationship with each other, so he ends up choosing Erica.
And then he talks about how much chemistry he and Daniel Sharman have on set and how awesome Daniel is, so that’s pretty cute. This whole interview is cute. He’s cute. But I digress— I’m pretty sure he talks about Scott’s sexuality in other interviews (I can almost visualize what he was wearing in one but I can’T FIND IT UGH) but I’m at work with limited resources, so this is all I’ve got for now :c