Such is the wild world of Anycast that it could either be the ISP or the infrastructure providers Fly uses that could be causing this.
If it is any solace, I routinely see traffic to Cloudflare’s network (presumably a much bigger Anycast deployment) from Mumbai routinely routed to Amsterdam, Paris, and London instead (unsurprisingly, happens with Fly Anycast, too: Global anycast routed to AMS).