I have just tested my presumption and it does appear that sadly Poll allows only one "guest" vote per poll created:

- created a new poll

- logged off the site on both my laptop and mobile devices

- checked the newly created poll on both devices as guest on both devices

- it allows view of the poll as guest on both devices

- it allows vote of the poll on both devices

- casted vote on mobile device (went all fine)

- refreshed home page of the site on laptop device

 - went to the the poll's page on the laptop

- and it does not allow me to cast vote as guest on the laptop even though I casted the vote as guest only on the phone device.

:-( :-(