The phrase "that silly sweater issue" can indeed be interpreted as sarcasm. This is because the use of silly in the sentence could be seen a dismissive.
Sarcasm is a form of speech where someone says something but means the opposite, often to mock or convey irony. In this context, the use of the term "silly" to describe the sweater issue implies a dismissive or mocking tone.
It suggests that the speaker doesn't view the sweater issue as trivial or unimportant, but rather, they are downplaying its significance or ridiculing it subtly.