He's not the only one... A lot of people are getting denied. There is nothing new, just a bigger crackdown which fits with new regulations, new visas, new systems... Certainly not on a blacklist but got a note and warned about it.
I doubt you're on a blacklist, but there may be notes on your immigration history profile. Your history of entries will stay in their system. This could cause issues when crossing the border, even if you have a visa. Ultimately, it's up to the immigration officer to decide whether to let you in.