Here are some possible reasons for people getting mad if you're really wondering why it happens:
unsolicited advice can make people feel stupid (you love to learn, not everyone does)
comments like yours can be used as a way of making fun of OP to disregard their point without actually interacting with it
being corrected on a slip up and not something you sincerely don't know can be annoying (either towards the person correcting you or towards yourself for "not knowing something this simple")
I don't know about others but my school life never taught me how to deal with criticism, if you made a mistake you didn't study properly and should go back to doing that instead of being explained what went wrong and why (this one might sound a worse than it really was but you get the point)
I'm not saying you did any of those things and I'm right there with you on learning but the knee-jerk reactions often do have a reason behind them. There's also the whole issue with how polarized social media is these days and the willingness to listen or admit to a mistake can be a difficult thing to stomach ("it's a sign of weakness").