Is it normal my girlfriend's mom squeezed my nipple ?

I've seen my girlfriend's mom a couple times but never really been inside her house because my gf lives with me. But yesterday, the most weird thing happened. So my gf and I went to the mall together and then we headed back to my house but on the way, I suddenly needed to take a shit and I couldn't hold it until we get home which was about 30 minutes away so my gf said I could use the bathroom at hers.

I couldn't even greet her mom properly because I was in such an urgent situation. I asked my gf where the bathroom was and ran straight for it. Luckily, I made it to the bathroom. After I'd emptied my bowels, I decided to take a quick shower to get rid of the smell. Not until I'd stepped inside the shower did I realize I'd forgot to ask my girlfriend for a towel. I thought she was in the next room so I asked loudly if she could fetch me a towel. I was behind the curtain, standing in the bathtub when I heard the bathroom door open, I thought it was my gf so I pulled the curtain aside but the person wasn't my gf, it was her mom. I startled and quickly retreated back behind the curtain and grabbed a part of it to cover my package. I tried to explain to her that I thought my girlfriend was outside but she just came closer to me and said 'nothing I haven't seen before' and as she shoved the towel into my hand, she squeezed my left nipple with her other hand. It was quite painful but both my hands was busy so I couldn't defend myself. I looked at her in shock but she just smiled at me and walked out of the bathroom. I looked down any my left nipple turned red, it was no joke ! What the hell happened ? Was that woman being serious ?