Many people mistakenly believe that eating chocolate causes pimples.
Tips
grammar
误认为 takes a clausal complement: 误认为 + [statement / identity]. Pattern: 把 X 误认为 Y = 'mistake X for Y'; 被 X 误认为 Y = 'be mistaken by X for Y.' 为 here is the literary copula 'to be' (as in 以为, 认为) — not 'because' or 'for.'
memory
Three-character compound built from 误 (wrongly) + 认 (recognize) + 为 (to be). It's the cognitive twin of 认为 rènwéi (to think / believe) — 认为 = think it is X; 误认为 = wrongly think it is X.