Both Wirecutter and Pocket-Lint discovered this the hard way while reviewing the HomePod. Apple confirmed to the former that this issue is happening -- but that "the marks can improve over several days after the speaker is removed from the wood surface." And if they don't go away, you can just clean the surface with "the manufacturer's suggested oiling method." In other words, it's on you to refinish any wooden platform that your brand-new $350 domestic speaker has injured.
As the tweet and other reports have noted, the HomePod leaves ring-shaped damage on wooden furniture. As Wirecutter pointed out, the smart speaker is fine to place on other materials like glass, granite counters, wood sealed in polyurethane and even venerable Ikea particle board, so resting your HomePod on one of those is a good idea. Or you could just buy any another modern smart speaker that doesn't threaten to scuff up furniture you spent money on.