Right – as github’s helpful autogenerated license summary says:
Conditions
- License and copyright notice
- Disclose source
- State changes
- Same license (library)
But those “changes” are if you are modifying the p5.js library itself. If you are just making a sketch and just using p5.js unchanged, you don’t have any changes to state. Still – you could change and redistribute p5.js if you wanted to, you just have to state what you did.