Until you and I receive the 8th gift of the Holy Spirit (reading mens' souls) I guess any conjecture on its sinfulness is...well...judgemental? Presumptuous? Folly? I don't know what to call it.
Until then, neither of us should hold our breath awaiting that gift, and neither of us knows why he did it, if it was even thought out beforehand, or simply an uncomfortable act performed in a moment of not knowing proper protocol to respect his hosts, or any reason whatsoever etc.
Frankly, I think internal and external enemies (who probably think they themselves have never committed any gaffes in their own lives) of Christ's Church have blown its significance way outta proportion simply to advance their own agenda.