Hello Attila
I think the problem here is in the explanations in each case. Let me try to clarify:
First of all, just to clarify, a Lightweight AP is any AP that is using a WLC. LWAPs can use multiple modes, which define how they operate. So, a FlexConnect and a Local AP are both LWAPs.
Now, a Local AP will always use the CAPWAP tunnel for both control and data traffic. A FlexConnect AP will always use the CAPWAP for data traffic, and will switch data traffic locally to reach the Internet. The text as Rene has written it is a bit misleading. It should read:
“The AP will always locally switch traffic between its own SSID and a local VLAN to reach the Internet (and other networks), even if the CAPWAP tunnel to the WLC is down.”
In the OCG, it considered “forwarding data normally” as forwarding data independently from the CAPWAP tunnel. Does that make sense?
Whenever you use a CAPWAP tunnel in local mode, and you send all data and control traffic to the WLC, you can do so for multiple SSIDs, so in the scenario in the diagram (local APs) this is doable.
However, for FlexConnect cases, you can only do this if you have mapped all of your SSIDs to the same local VLAN. If not, then you must use a trunk for local switching to take place. This scenario is not specified in the OCG, and it may just be an unfortunate omission. However, you are correct in your understanding. This NetworkLessons note also sheds more light on the switchport mode for FlexConnect APs.
I hope this has been helpful!
Laz