Thanks for asking. It’s metal. However, the signal from SmartThings to the bulb (Wi-Fi) is fine.
There is a problem (as documented, for example, in the Matter Playground thread) where the hop between the Zigbee (or Z-Wave, or Matter) controller to SmartThings hub, then to routines/rules, then to LIFX (over Matter) is not reliably fast. Smooth dimming and fast lighting scene switching on SmartThings appears to be almost impossible to achieve.
LIFX Switch with Matter binding to LIFX bulbs (including the bulbs in the wall lamp arm depicted) is pretty close to instantaneous, after it settles down from initial pairing. In that case, SmartThings plays no role. After initial pairing, I have observed extreme lag, sometimes 3-5 seconds, between the LIFX Switch button press and the LIFX Matter lights actually responding. If the network is rebooted or if Internet is disconnected, then toggle on/off with direct Matter binding works fast. I do not have a satisfactory explanation for this initially, but fortunately it settles down.