The story
Unclear. Attested in English from the 1920s, after a French source. A range of candidates has been proposed, including Chinese 木薑子 /木姜子 (mùjiāngzǐ) and 山胡椒 (shānhújiāo), with possible influence from May, from the month of flowering. However, given the provenance, Vietnamese may be a more likely source.
Etymology from Wiktionary, CC BY-SA 4.0.