Crocombe, 24, was shown a straight red card in the 87th minute of the non-league fixture, which ended 2-1 to Salford.
Park Avenue secretary Colin Barker was quoted as saying by BBC Sport: "He was told by the steward twice not to do it and he went ahead and had a pee. He went to the side of the stand as I understand it.
"I didn't actually see it, but the referee definitely sent him off for it because he was alerted to it by his linesman."
New Zealander Crocombe, who has previously represented Oxford United, joined Salford in May.