Imagine there is a lot of possibilities:
Wheel weight knocked off on the change, tire switched sides and now running backwards, slight bent rim/balance issue that only shows up on the steering axle, junk fell between the rim and the wheel when mounting, wheel loose and ready to fall off

etc.
Of course it might just be a coincidence, and you just happened to get a bubble/delamination in a tire at the same time as the rotation.
There's a few things you could check by eye, but it would be cheap and quick to get them rebalanced and checked over. I've never had vibration from an alignment issue.