The article counts one day before and after the actual full moon day as close enough. So this "rare" occurance will happen about 10% of the years.
The astronomical definition of “full moon” is related to position, not illumination. A lunar eclipse only occurs during a “full moon”. The timing of the “full moon” is 6:17 AM on Sunday, which means at moonrise on Saturday is closer to the “full moon” than on Sunday night. Generally, the moon will appear “full” for a day or so before and after the nominal date of a full moon. I agree it’s not particularly rare, but they are trying to get people interested.
Time of moonrise and percent illuminated at the U.S. Naval Observatory, in Washington DC for Friday-Sunday:
-—DATE— // TIME // Percent Illuminated.
2024-Jul-19 // 19:39 // 97.23765
2024-Jul-20 // 20:31 // 99.57803
2024-Jul-21 // 21:14 // 99.19673
2024-Jul-22 // 21:49 // 95.98919
55 * 365.25 / 29.54 = 680.0524712255
Happens about every 11 years.
52 * 365.25 / 29.54 = 642.9587000677