His initial tweet was shared more than 5,000 times.
Almost two hours later, Mr Johnston told his followers he was OK, his friends had unzipped him and he had "never been so happy to see the rain".
However, it is understood his original tweet may have been a prank.
Johnson told the Daily Record he had already left the park when he created the Tweet.
"It is everywhere online... I just tweeted it for a laugh. I didnt think it would spiral out of control. I barely use Twitter. Thats probably the first tweet Ive sent in ages."
"I dont feel bad about it. I cant stop laughing - its the only thing that made me laugh all weekend."
Organisers of the festival, now in its 22nd year, hailed this year's event a success despite lengthy delays and scenes of chaos as cars trying to leave the site got stuck in thick mud.
- PAA