Yes. If you search for such result on the internet, You will find plenty of users' account was frozen. Coinbase has a big list of reasons that can cause freezing your funds. Most probably, your friend deposited Crypto in Online casinos or paid for adult content and services. Or maybe invested in pyramid Schemes. Most Users do not read the User agreement before they sign up.
Coinbase Prohibits Plenty of Businesses like Investment and Credit Services, Restricted Financial Services, Intellectual Property or Proprietary Rights Infringement, Counterfeit or Unauthorized Goods, Regulated Products and Services, Drugs and Drug Paraphernalia, Pseudo-Pharmaceuticals, Substances designed to mimic illegal drugs, Adult Content and Services, Multi-level Marketing, Unfair, predatory or deceptive practices, High-risk businesses.
Coinbase itself mentioned why they could freeze your funds:
We are required to comply with an order from a court or other authority that has jurisdiction over Coinbase which compels us to restrict access to funds.
We are required by law to freeze or block assets in compliance with a sanctions program, including, but not limited to sanctions programs administered by the U.S. Office of Foreign Assets Control (OFAC).
For more detailed information, I recommend you read this:
[1] Does Coinbase freeze accounts?
[2] Coinbase Prohibited & Conditional Use Policy
[3] Coinbase User Agreement Read from 6.1 to 6.3 SUSPENSION, TERMINATION, AND CANCELLATION.
I would have to read the user agreement from now on before joining or using an exchange, because what's the point of using a decentralized network if it isnt decentralized?
If it is controlled by other external bodies, even upon completion of my KYC verification and adherence to its functions for my benefits, why would my account be frozen without an explanation as to why?
Unless I falter, still a notification should be sent out to me the user, because it is not only such app that I have to adhere to its user agreement. I may not even remember what I read on its user agreement page nor even remember the limitations imposed to prompt such a freeze of my account. What now makes them better than using a fiat system?