I agree with Peter that Steward John Stewart was probably rescued in Lifeboat # 15. He was specifically recognized and mentioned by fellow Steward Samuel Rule in his British Inquiry testimony. As Peter indicated, later information from Steward's family also indicates that Stewart left in a lifeboat rather than being pulled from the water as was claimed in the press.
It was mentioned in the inquiries by Able-Bodied Seaman Evans that he recognized a "steward, young Stewart" who was pulled from the water into Lifeboat # 14. I believe this to be a case of mistaken identity, or that Evans said that a "young steward" was pulled from the water and that the American's questioning him simply misunderstood his accent. Steward Harold Phillimore was fairly young (23) and was one of those we know to have been rescued in # 14, so perhaps this is who he was referring to? This is all speculation. We have two different sources (one possibly mistaken) in the inquiries giving totally different explanations of how Stewart was rescued. We cannot be certain.
In any case, if Jack Stewart was rescued in a lifeboat rather than being pulled from the water, I find his story of Thomas Andrews last being seen staring at the painting in the Smoking Lounge to be somewhat dubious. It is a powerful image, but if Stewart actually did see him there *and* left in Lifeboat # 15, then the sighting had to have been prior to the time the lifeboat left, approximately at or around 1:32 AM, nearly 48 minutes before the ship sank.