Definitely "seems" like you have a lightweight image on the AP. the "model" if that's in fact the exact model number: AIR-AP1131AG would indicate stand-alone, however from what you've described it must have lightweight image on it.
You will not be able to telnet/ssh/gui manage the AP in lightweight unless telnet/ssh enabled at WLC first. So, to "verify", you should run a "show ver" from the AP console.
If you're image has a k9w7, it is standalaone. k9w8 would indicate a lightweight version.
Stand-alone for 1131: c1130-k9w7-tar.124-10b.JA3.tar
Lightweight for 1131: c1130-rcvk9w8-tar.124-10b.JDA.tar
That is not a standalone ap. if you are able to do the debug capwap console cli, it's a lightweight access point. You need to follow the link that was posted to convert it. take a look at the model number if this was a brand new ap. if it shows LAP1131 it's lightweight. It should just show AP1131.