No it is not. The production rule for function call is given as

function-call   ::= fn-name { expression }

That says, that the arguments of the call are expressions. 3 + 4 is an expression, so interpreting the input f 2 3 + 4 as equivalent to f 2 (3 + 4) is valid according to the grammar. That the grammar lists function-call (only) as an option for factor does not change that. The grammar is simply ambiguous. In more ways than this.

It is defined uniquely by the grammar; function calls have highest precedence.

I think I recall coming across this because I was failing some tests due to whichever order the tests expected. Maybe I just noticed it from the specification though. Unfortunately it was so long ago that I don't remember.

It's probably implementation-dependent, and there do not seem to be tests with it currently.

Did you finish the kata? Which precedence order was correct?

I haven't completed the kata, but I would take f 2 3 + 4 as (f 2 3) + 4, in the same manner that 23+5 is taken as (23)+5

love the kata.
There is so much in there to learn.
Grammar transformations, applying Visitor pattern, ...

There are some ambiguities such as order of evaluation, e.g. "4 / 2 * 3" is 6.0 according to the kata, but could be 2/3 also,
but these can be resolved through debug statements.

I do not believe the problem description uniquely specifies the result of the following:

fn f x y => x * y
f 2 3 + 4

This could either return 10 or 9, depending on whether it is evaluated as (f 2 3) + 4, or f 2 (3 + 4).

Function calls should thus be added to the precedence table.

Full LR parser for learning purposes

Don't parse the output of ls: http://mywiki.wooledge.org/ParsingLs