Adding condensed milk to coffee is not a new thing and maybe you’ve already had a Vietnamese Coffee, Cafe Bonbon or Cafe Canario, but this latte as it’s showing up right now is a slight variation on these. First of all, it’s using espresso instead of drip coffee and it’s not using just condensed milk but it balances it out with textured milk.
There are also mentions about coffees with the same recipe but different names like Havana Latte, Cuban Latte, you can probably see a pattern here.
There’s not a lot of information out there about Spanish Latte so it’s really hard to pinpoint where it first started. The place that shows up most often in my searches is Think Coffee in NYC, although there are a lot of mentions about the drink in all corners of the continental USA.