Good catch!
This has been addressed by the following github commit: https://github.com/Azure-Samples/digital-twins-samples/commit/a7f1716becdbb27c29d837c209be989f2549d99a
Casting your temperature value as it's expected data type (float) fixes the issue:
AdtUtilities.UpdateTwinPropertyAsync(client, parentId, propertyPath, operation["value"].Value<float>(), log);
Alex
Digital Twins PM Team