Am I a bad mom? Genuine answers only please...?

So today I was out with my boyfriend and my two year old son at Sonic. I got my son some chicken strips and water.. i ordered myself a strawberry creamslush and gave him some of it. Well i only intended to give him a little and this was my first time giving him something like that so i didnt know he was gonna have an emotional meltdown when he got a little taste and then was told no more its mommies. Anywho he has this emotional meltdown and after about a min. of screaming and crying i decided we needed to head back home so we got up to walk away. as i am walking away with the stroller and my boyfriend was throwing all our trash away this lady in this car says "take care of your kid you f****** B*****." I was of course stunned and didn't even know what to say. Even though I know she was being trashy in the back of my mind I'm wondering was i wrong for ignoring his crying? What should i have done? it just bothers me a little and i just wanna make sure I'm being a good mommy.