That's a hypothesis amongst others, but it's just that, with essentially no hard evidence backing it up.

And there's counter-evidence (if mostly circumstantial) in that the first known knitted artefacts are from centuries later, to say nothing of knitting spools which they would predate by some 1300 years.

This hypothesis also lacks a lot of explanatory power e.g. why did some of them find (and take) room in coin hoards? Why have they been found all over Gallia, Germania, and Britannia, but not Italia, Hispania, or the Oriens?