Forth examples can be more terse than C examples because Forth uses a stack for storing and manipulating intermediate values while C uses infix expressions and temporary variables. It's not just "shorter" syntax, it works in a different way. My real point with the Forth/C comparison is not that the Forth code is smaller but that it clearly has fewer "moving parts"- the for loop is simpler and provides fewer options, there's no need for special syntax to index array pointers, there's no need to specify method signatures, etc.

Language design is not simply a balance between terseness and verbosity, it's a complex series of tradeoffs between many paradigms and features- some allow you to express ideas more succinctly, flexibly or reliably.