The stem(s) are fused and thick into a single stem - any thoughts ?
There were a few other single flowers with big stems too from this plant.
Anyone spraying herbicides in the area? 2,4-D can do that in low doses.
This might be one for the weed forum though as dandelions aren't native.
The neighbor sprays the cracks in the paths - how far can the poisons go ?
How far does the wind blow? Anyway, yes, herbicides can be windblown some distance.
This is an impressive example of fasciation. It may be caused by herbicide but dandelions are fairly prone to it naturally.
Here is a link that might be useful: Fasciation