Apple TLD has seen that Twitter is rolling out an option to follow somebody that appears in your feed straight from their tweet.
If their tweet is retweeted by someone you follow in your feed or is suggested to you, tap the small follow icon in the row of icons below the tweet to quickly follow the user. You can tap this again to unfollow them.
We can vouch that this feature is on two of our accounts when using the iOS app, but not available on the Twitter Web App.
It’s certainly a handy feature but could result in accidental follows for accounts you don’t wish to see in your feed.