Marx borrowed most of his ideas from Frenchmen like Fourier and even a Scot like Robert Owen, neither of whom was Jewish (and neither was Marx, in any educational or cultural sense).
It doesn’t matter since he was, ethnically. That’s all that matters to the anti-Semites of Europe. Don’t think for a moment that was not a factor in the clash between Reds and National Socialists in the 30s.