No, they did not. They made it free to download, but open-access† licensing would permit third parties to legally mirror it on servers that don't block access from Algeria or Switzerland or privacy-focused browsers, and so far that licensing hadn't happened. I'm happy to see that apparently it's happening today.

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† As defined in the Berlin Declaration 22 years ago: https://openaccess.mpg.de/Berlin-Declaration

So that's what this wording means:

> Making the first 50 years of its publications and related content freely available expresses ACM’s commitment to open access publication and represents another milestone in our transition to full open access within the next five years.

( from https://www.acm.org/articles/bulletins/2022/april/50-years-b... )

I wouldn't have understood that nuance without the context given by your comment, but in my developer mind I analogize "freely available" to a "source available" license that they took on, as a step towards going open access ("free and open source") over time. I'm also happy to see that that transition seems on track as planned.