From Thai-Language .Com

[phomsanuk]

This word is believed to have originated as a transliteration of the French pronunciation of the French word "Français." The French were the first group of Westerners to be known amongst the Siamese. ฝรั่ง is now used to refer to any foreign object adopted into Thai culture.

[zzaa09]

The Portuguese and Dutch made considerable Western contacts long before the French.

[Crossy]

There are already multiple discussions on the origin of the word farang, here is one

Another is not required.