0x60 is the hexadecimal representation of 96 (base 10).
In this context, it means the data part of the string is 96 bytes (or three 32 bytes words) away from the start of the arguments (discarding the first 4 bytes for the function id, count 3 words and this is where).
Based on the example of the docs:
start counting here:
First 32 bytes, offset is 0:
Second/offset 32 == 0x20
Third: offset 64 == 0x40
Then here starts the part pointed by the first 0x60, offset 96==0x60