The ability to subitize can be developed, and uses a student’s pattern recognition skills. Part part whole understanding is usually used to subitize numbers over four or five.
This means a student looking at this pattern doesn’t usually see 7, but instead 1 and 6, or maybe 2 and 5.
This is one of the reasons larger patterns shouldn’t be used until students are familiar with various representations of numbers 1 to 5. When two colours are used in patterns, they also draw attention to smaller anchors and make the parts more obvious.