From pollsters Find out Now, the above and:

We ask respondents how likely they are to vote in the Scottish Parliament election on 7th May. For those who give a 7 or above, we then ask their vote choice

If a respondent answers ‘Don’t know’ they see an additional question, prompting them again to give an answer. If they then give a valid vote choice they are included in the final calculation, but if they answer ‘Don’t know’ again (or ‘Would not vote’) they are excluded from the final headline calculation.

Source: https://findoutnow.co.uk/blog/scotland-vi/

Find Out Now is registered with the British Polling Council so this is probably a more accurate prediction.

Notably, the sample was not weighted according to the 2014 Referendum result.