He could have spat it out all over the handcuffs and melted them away like it was acid.

It's the thought of it. Ethan lived there, he might be immune to it like everyone else in the station apparently was.
"STAY PUT ETHAN. I'll go get you some coffee. :D"

I lol everytime he says "stay put" -- like he's going to get up and go for a walk when he's cuffed to the desk. Oh Jayden, you so silly.