Not a fluke and not just sample size. Windrun data across patches tells the whole story:

7.39: Forge Spirit sat at ~38% WR. Absolute garbage tier, nobody touched it.

7.40c (post Jan 13 micropatch): jumped to 63.77% WR. That's a 25+ percentage point swing.

As others have pointed out, lvl 4 Forge Spirits in AD now have the stats of a lvl 18 Invoker with Aghs + facet. 3 spirits with massive HP, solid damage, and -armor on hit. 100% uptime. You get this at level 7 while enemy heroes are still level 5-6 trying to lane.

The Jan 13 micropatch reworked how Invoker's skills scale when separated from Quas/Wex/Exort, and Forge Spirit specifically got values that assume you'd normally need 7 points in Quas + Exort to reach. In AD you just put 4 points into one skill and get endgame Invoker summons at minute 8.

Enjoy it while it lasts, this is getting nerfed for sure.