My middle daughter refers to us as 'you guys' on occasion, but she is thirty-eight.
If she had said it when she was thirty years younger, I would have suggested that it was a little unsuitable, although I would not have been offended - but guiding children about appropriate behaviour as they grow up is an important part of parenting.
You don't say how old you are, but it does appear that your parents were upset - and that may be down to cultural concepts of respect.
What is rude to one parent may not be to another, but the only parents whose opinions matter the most to you are your own - so take their reaction on advisement, and know not to say it again.