This is similar to MQTT-452.

Reason Code 0xA2 is listed for both DISCONNECT and SUBACK in Table 2-4 and for SUBACK in 3-10, but I don't see a reference to its use with SUBACK only DISCONNECT on Lines 1608-1610:

"If the Server receives a SUBSCRIBE packet containing a Wildcard Subscription and it does not support Wildcard Subscriptions, this is a Protocol Error. The Server uses DISCONNECT with Reason Code 0xA2 (Wildcard subscription not supported) as described in section 4.13."