Is digging into the pressure point above the knee to pass guard legal?

During rolling at the end of class on Thursday I was in my opponent's guard and in order to pass I did something I had learned from my brief stint learning MMA under a submission wrestler: I took my elbow, placed it (not a strike) against his inner thigh just above the knee, and then applied pressure.

He yelled out a bit in pain and then told me: Hey don't do that I'm not sure if its legal in BJJ in the first place but we train "nice" here. He also said if I do that to someone else that they might get mad and just hit me or something.

I certainly won't be doing that to him again as it seemed to greatly upset him, and I don't want to upset my fellow students.

Not quite sure what he meant on the "nice" remark as I've seen instructors show ways to make your opponent uncomfortable in various situations. (E.g., using your forearm to sort of grate their face on the mat in some positions, or cutting off some of their head's blood supply with the cross-face, etc.)

To my knowledge what I did doesn't cause injury, nor is it a strike, so I hadn't thought not to do it.

I meant to ask my instructor but forgot, and want to ask here in case I forget by the next class: Is what I did legal in BJJ competitions?
Is it frowned on?