There's a number of different stimulants and non-stimulants. "The meds" are not a thing.
And Guanfacine is certainly a stimulant. It is an agonist of the α2A-adrenergic receptor. https://en.wikipedia.org/wiki/Guanfacine
The drug antagonizes the adrenaline receptors. Adrenaline stimulates people.
They are selling it as a non-stimulant drug because people are stupid.
Buproprion and clonidine are commonly prescribed for ADHD in the US.
If you take ADHD stimulant meds and get high, you probably don’t have ADHD.
Also, not sure what epilepsy has to do with anything here.
In general: High generic correlation and interesting drug interaction https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10049646/ (but I'm not sure if that's what OP was thinking of)