Well it can't be ONLY wfh. I think they meant "primarily". But more commuters choosing to drive is impacted by fewer people driving in due to WFH. The traffic was light, so they drove. Now traffic is normal again.
If its miles total, I would chock it up to people doing more leisure travel, seeing family etc.
I don't think RTO is in full swing in such force that its commuter miles, so I'd say you're seeing a big uptick in leisure travel right now, which makes sense, as more and more people are becoming comfortable with this again