OK, I youtubed it.
No, I am totally wrong. You know what LH did wrong? He did not let Kimi just pass. No, he stayed on the dry line full on, just before the next corner Kimi had to switch from the wet to the dry line onto the ideal line which, whereas LH just kept going. I think that was the crucial moment for the marshals. LH did not really have the intention to give back his position. At least, he did it in a very unmotivated manner. Kimi could only pass him in a way that he HAD to lose it again in the next corner.
So, IF LH had to give back his first position because of cutting the chicane (which is another discussion), then I think it´s not so strange that he got a penalty, really...