Weather on Mull
Tandemrotor
1 The report doesn't give heights. One walker reported that, in ten metres viz, he thought the aircraft was going to hit him but still couldn't see it.
2 It is of course possible but there is little to suggest that it was.
3 They didn't describe visibility as 'coming and going', they reported variously 'thick' or 'dense' fog, viz 15 metres, being unable to see the aircraft because it was 'up in the mist'.
4. You got me. I should have said a very high probability, see comments from BOAC and SFFP