[threeseed]

If you think about what you asked Siri it's a sensible response.

You didn't ask her to set an alarm for 6:15am. You asked her to turn on an existing 6:15am alarm.

Which since I am assuming it didn't exist Siri asked what others you did want to turn on.

[fetus8]

Late response, but here's the thing...that alarm does exist and is listed off when Siri goes through all the existing alarm options that can be turned on...