The rule is: "i before e, except after c, or when sounding like 'ay' as in 'neighbor' and 'weigh'."
So...
* "Before a short i spelled e" is not always true. There are exceptions to this rule, like "friend" and "science."
* "Before a short i spelled e" is generally true when the "e" is followed by a consonant, like in "believe," "chief," and "field."
Let me know if you'd like to test out some words to see if the rule applies!