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Yes it's a root. Sometimes they do decide to go up for some reason. I have one with about 6 roots reaching higher than the leaves, I missed a new spike in amongst them as a result.
The growing tips of roots are either green or redish list yours while the older part of the root is silvery like you see on yours. Also the tip is very rounded.
A spike will be similar colour as the growing tip, but will not turn silvery. It also had a 'mitten' like shape at the tip.