Well yes and NO, from the pic the nostrils look clear except the first pic, he was an awful mess but that's because he had some mud around him. LOL, So A sinus infection would definitely be Questionable...They'd still have some basics. I'm concerned, since she did successfully aspirate it, and did find a collection of pus, that it's more than just a sinus infection. My experience (with mammals, granted) is that a deep collection of pus is some sort of abscess... I'd think a sinus infection would be limited to inflammation and mucus in the sinuses?
I would be looking more into it, such as Ears, EYES is there bubbles or white gooy stuff coming out of it? Look inside the Mouth? What does that look like? Smelling him, smell his breath? etc... Is there any other signs, like staggering while walking. how is he in the water? Does he swim OK. Is he eating, is he cleaning his own nose, is he activite. ETC.. I mean the more information the better and I just feel like there's not enough information before making any calls.