How may 'mope' be an Ideophone?

[ Etymonline : ] >1560s, "to move and act unconsciously;" 1580s, "to be listless and apathetic," the sound of the word perhaps somehow suggestive of low feelings (compare Low German mopen "to sulk," Dutch moppen "to grumble, to grouse," Danish maabe, dialectal Swedish mopa "to mope"). [...]

How may 'mope' be an Ideophone, as the bold alleges?

Solution 1:

There are several English words beginning with "mo" that evoke sadness: mourn, moody, morose, moan. The author of the definition you quoted may associate the sound "mo" with sadness for that reason.

This is an example of clustering:

Words that share a sound sometimes have something in common. If we take, for example, words that have no prefix or suffix and group them according to meaning, some of them will fall into a number of categories. So we find that there is a group of words beginning with /b/ that are about barriers, bulges and bursting, and some other group of /b/ words that are about being banged, beaten, battered, bruised, blistered and bashed.

Source: https://en.wikipedia.org/wiki/Sound_symbolism#Clustering

I am not sure if this is an ideophone or not, but the definition you quoted does not use that word, it merely says that the sound of the word suggests low feelings.