I think there is some truth in it, actually.
My parents say they're not bothered what we do as long as we're happy blah blah blah, yet my sister dropped out of uni and decided to stay at her job as a bar person for a while and my parents were both disappointed. My mum, because she had to drop out of college to be a parent, and my dad because all his life he has done a boring-but-paid-well-and-secure job and I think he wants better for us. My dad also wanted to join the navy and is over the moon that my sister is now in the army.
With me, my parents had two children so wanted me to stay with two children. I could say they didn't make their views known, but they did, with endless comments on how people can only afford to provide for two children, that supermarket shopping is good for four and a bit of a pain for five, etc. Also, both my parents were over the moon when I had a boy (the first one that is) because they didn't have a son and would have secretly liked one. My dad went mad when I told him I was pg at the age of 19, and actually stated that "kids ruin your life". I don't think he regrets having a family (though tough luck if he does) but he does regret some of the things he hasn't done, and wanted me to do.
With studying, my mum has an OU degree and wants me to get an OU degree (having already done a few courses and considering 'conventional' uni), but because her degree hasn't gotten her a decent job like she hoped for, she now says any degree is a waste of time. My mum is an 'English' person, my dad a 'Maths' so we all frequently have the arts/science courses are better/harder conversations.
My mum and I are very (unspokenly) competitive, which is obviously good and bad...
So yeah, there's tons of other examples (smacking children, being a sahm, friends, routines etc) but I do think there is some truth in parents trying to compete with/recreate their children based on what they would have liked to do with their lives.