Using my own words, I see the rule as:
No single line of three or more frogs may exist if at least one of the frogs does not touch a minimum of three other tiles.
Am I interpreting this correctly
No: consider a ring of 6 frogs (around an empty center hole). That does not conform to your condition (every frog touches exactly 2 other frogs, none touches 3), yet it is a legitimate configuration.
EDIT: Perhaps I misunderstood what you meant by "line"; if you don't mean to include rings, then perhaps you're closer than I thought to understanding.
if not can anyone explain to me what the string rule means in "layman's terms".
I explained it in my review as:
If there are 4 frogs A, B, C, D such that A only touches B, B only touches A and C, C only touches B and D, then that is called a "string" and is not permitted.)
I.e. something like the following is illegal:
Or putting it REALLY simply/informally: you can't have a "long tail" with 4 frogs in the tail.
Does that help?