Not really, McDowell says it most likely is, but he's "not fully convinced". Langbroek says it's plausible his blog goes on the explain why and show other debris was found in the region, references McDownell, the anonymous Twitter account, Arianespace's doubt.
Langbroek even simulated the situation (in TU Delft Astrodynamics Toolbox[0]) with known information about recent flights. His blog post is pretty thorough.[1]
It's a shame Arianespace (who.. you know, may be worried about reputation or liability) hasn't just posted an image of the SYLDA shell they say it isn't.. that would clear up the speculation.
