Need some advice on if this is normal.

My child has been making patterns lately by lining up colored toys or stacking blocks. The patterns are typically done with blocks or the same size and shape and they will alternate colors such as green red green red or blue yellow red blue yellow red. Is this normal or something I should bring up to ped? I have had concerns about them displaying possible signs of autism, but they passed the 18m test. I just feel like this is really odd for a child their age.