Just my opinion but the activity itself between two or more males whether spontaneous, planned, coordinated or unplanned (jerking with or in front of another guy) is gay, regardless of whether you're straight or not.
It doesn't matter what kind of porn you're watching, if you have your cock out and you're jerking off with another guy you should be prepared for or anticipate that the other guy may want it to go further.
If a female offered to masturbate with you while you were watching straight or lesbian porn, would you just sit there without pushing the envelope?
If you're having a hard time finding takers, go figure right?