Check this method.

This method from zinc project:

testMultiValues
	| dictionary values keys |
	dictionary := ZnMultiValueDictionary new.
	dictionary at: 'foo' add: 1; at: 'foo' add: 2.
	self assert: (dictionary at: 'foo') = #(1 2).
	self assert: dictionary keys asArray = #('foo').
	values := OrderedCollection new.
	keys := OrderedCollection new.
	dictionary keysAndValuesDo: [ :key :value | keys add: key. values add: value ].
	self assert: values = (OrderedCollection with: 1 with: 2).
	self assert: keys = (OrderedCollection with: 'foo' with: 'foo')

is converted to it:

testMultiValues_amp_L20
	<madeBySmallAmp>
	| dictionary values keys |
	dictionary := ZnMultiValueDictionary new.
	dictionary := dictionary
		at: 'foo' add: 1;
		at: 'foo' add: 1.
	values := OrderedCollection new.
	keys := OrderedCollection new.
	 dictionary
				keysAndValuesDo: [ :key :value | 
					keys add: key.
					values add: value ] 

Line 5 of Which does not look correct. Why the dictionary variable is set to the result of Dictionary>>#at:add: ?

Start with the original testMultiValues example in the issue and compare it with the generated testMultiValues_amp_L20 output. Inspect how small-amp converts the Dictionary>>#at:add: expression, then determine the expected transformed test and verify that the dictionary assignment and repeated values match the source behavior.